Phoenix has a string s consisting of lowercase Latin letters. He wants to distribute all the letters of his string into k non-empty strings a_1, a_2, ..., a_k such that every letter of s goes to exactly one of the strings a_i. The strings a_i do not need to be substrings of s. Phoenix can distribute letters of s and rearrange the letters within each string a_i however he wants.

For example, if s =  baba and k=2, Phoenix may distribute the letters of his string in many ways, such as: 

  * ba and ba
  * a and abb
  * ab and ab
  * aa and bb



But these ways are invalid: 

  * baa and ba
  * b and ba
  * baba and empty string (a_i should be non-empty) 



Phoenix wants to distribute the letters of his string s into k strings a_1, a_2, ..., a_k to minimize the lexicographically maximum string among them, i. e. minimize max(a_1, a_2, ..., a_k). Help him find the optimal distribution and print the minimal possible value of max(a_1, a_2, ..., a_k).

String x is lexicographically less than string y if either x is a prefix of y and x ≠ y, or there exists an index i (1 ≤ i ≤ min(|x|, |y|)) such that x_i < y_i and for every j (1 ≤ j < i) x_j = y_j. Here |x| denotes the length of the string x.

Input

The input consists of multiple test cases. The first line contains an integer t (1 ≤ t ≤ 1000) — the number of test cases. Each test case consists of two lines.

The first line of each test case consists of two integers n and k (1 ≤ k ≤ n ≤ 10^5) — the length of string s and the number of non-empty strings, into which Phoenix wants to distribute letters of s, respectively.

The second line of each test case contains a string s of length n consisting only of lowercase Latin letters.

It is guaranteed that the sum of n over all test cases is ≤ 10^5.

Output

Print t answers — one per test case. The i-th answer should be the minimal possible value of max(a_1, a_2, ..., a_k) in the i-th test case.

Example

Input


6
4 2
baba
5 2
baacb
5 3
baacb
5 3
aaaaa
6 4
aaxxzz
7 1
phoenix


Output


ab
abbc
b
aa
x
ehinopx

Note

In the first test case, one optimal solution is to distribute baba into ab and ab. 

In the second test case, one optimal solution is to distribute baacb into abbc and a.

In the third test case, one optimal solution is to distribute baacb into ac, ab, and b.

In the fourth test case, one optimal solution is to distribute aaaaa into aa, aa, and a.

In the fifth test case, one optimal solution is to distribute aaxxzz into az, az, x, and x.

In the sixth test case, one optimal solution is to distribute phoenix into ehinopx.
import java.io.Writer;
import java.io.BufferedWriter;
import java.io.OutputStreamWriter;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.IOException;
import java.io.InputStream;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.InputMismatchException;
import java.util.*;
import java.io.*;
import java.math.*;

public class C{
  static class ProblemSolver{
    public void solveTheProblem(InputReader in,OutputWriter out, NumberTheory nt){
      int test=in.nextInt();
      while(test-- >0){
        int n=in.nextInt();
        int k=in.nextInt();
        String s=in.nextLine();
        char c[]=s.toCharArray();
        Arrays.sort(c);
        s=new String(c);
        String ans="";
        // System.out.println(s);
        if(k==1){
          System.out.println(s);continue;
        }
        if(s.charAt(0)!=s.charAt(k-1)){
          System.out.println(s.charAt(k-1));
          continue;
        }
        else{
          ans+=s.charAt(0);
        }
        if(k==n){
          System.out.println(ans);continue;
        }
        int l=s.lastIndexOf(s.charAt(k));
        // System.out.println("l: "+l);
        if(l==n-1){
        for(int i=k;i<=l;i+=k){
          ans+=s.charAt(k);
        }//babaa aaabb
        // System.out.println("---"+ans);
        // aabb
        // a
        l+=1;
      }
        else{
          l=k;
        }
        ans+=s.substring(l);
        System.out.println(ans);
      }
    }
  }

  public static void main(String[] args){
    InputStream inputStream=System.in;
    OutputStream outputStream=System.out;
    InputReader in=new InputReader(inputStream);
    OutputWriter out=new OutputWriter(outputStream);
    NumberTheory nt= new NumberTheory();
    ProblemSolver problemSolver=new ProblemSolver();
    problemSolver.solveTheProblem(in,out, nt);
    out.flush();
    out.close();
  }



  static class InputReader {
    private boolean finished = false;

    private InputStream stream;
    private byte[] buf = new byte[1024];
    private int curChar;
    private int numChars;
    private SpaceCharFilter filter;

    public InputReader(InputStream stream) {
      this.stream = stream;
    }

    public int read() {
      if (numChars == -1) {
        throw new InputMismatchException();
      }
      if (curChar >= numChars) {
        curChar = 0;
        try {
          numChars = stream.read(buf);
        } catch (IOException e) {
          throw new InputMismatchException();
        }
        if (numChars <= 0) {
          return -1;
        }
      }
      return buf[curChar++];
    }

    public int peek() {
      if (numChars == -1) {
        return -1;
      }
      if (curChar >= numChars) {
        curChar = 0;
        try {
          numChars = stream.read(buf);
        } catch (IOException e) {
          return -1;
        }
        if (numChars <= 0) {
          return -1;
        }
      }
      return buf[curChar];
    }

    public int nextInt() {
      int c = read();
      while (isSpaceChar(c)) {
        c = read();
      }
      int sgn = 1;
      if (c == '-') {
        sgn = -1;
        c = read();
      }
      int res = 0;
      do {
        if (c < '0' || c > '9') {
          throw new InputMismatchException();
        }
        res *= 10;
        res += c - '0';
        c = read();
      } while (!isSpaceChar(c));
      return res * sgn;
    }

    public long nextLong() {
      int c = read();
      while (isSpaceChar(c)) {
        c = read();
      }
      int sgn = 1;
      if (c == '-') {
        sgn = -1;
        c = read();
      }
      long res = 0;
      do {
        if (c < '0' || c > '9') {
          throw new InputMismatchException();
        }
        res *= 10;
        res += c - '0';
        c = read();
      } while (!isSpaceChar(c));
      return res * sgn;
    }

    public String nextLine() {
      int c = read();
      while (isSpaceChar(c)) {
        c = read();
      }
      StringBuilder res = new StringBuilder();
      do {
        if (Character.isValidCodePoint(c)) {
          res.appendCodePoint(c);
        }
        c = read();
      } while (!isSpaceChar(c));
      return res.toString();
    }

    public boolean isSpaceChar(int c) {
      if (filter != null) {
        return filter.isSpaceChar(c);
      }
      return isWhitespace(c);
    }

    public static boolean isWhitespace(int c) {
      return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
    }

    private String readLine0() {
      StringBuilder buf = new StringBuilder();
      int c = read();
      while (c != '\n' && c != -1) {
        if (c != '\r') {
          buf.appendCodePoint(c);
        }
        c = read();
      }
      return buf.toString();
    }

    public String readLine() {
      String s = readLine0();
      while (s.trim().length() == 0) {
        s = readLine0();
      }
      return s;
    }

    public String readLine(boolean ignoreEmptyLines) {
      if (ignoreEmptyLines) {
        return readLine();
      } else {
        return readLine0();
      }
    }

    public BigInteger readBigInteger() {
      try {
        return new BigInteger(nextLine());
      } catch (NumberFormatException e) {
        throw new InputMismatchException();
      }
    }

    public char nextCharacter() {
      int c = read();
      while (isSpaceChar(c)) {
        c = read();
      }
      return (char) c;
    }

    public double nextDouble() {
      int c = read();
      while (isSpaceChar(c)) {
        c = read();
      }
      int sgn = 1;
      if (c == '-') {
        sgn = -1;
        c = read();
      }
      double res = 0;
      while (!isSpaceChar(c) && c != '.') {
        if (c == 'e' || c == 'E') {
          return res * Math.pow(10, nextInt());
        }
        if (c < '0' || c > '9') {
          throw new InputMismatchException();
        }
        res *= 10;
        res += c - '0';
        c = read();
      }
      if (c == '.') {
        c = read();
        double m = 1;
        while (!isSpaceChar(c)) {
          if (c == 'e' || c == 'E') {
            return res * Math.pow(10, nextInt());
          }
          if (c < '0' || c > '9') {
            throw new InputMismatchException();
          }
          m /= 10;
          res += (c - '0') * m;
          c = read();
        }
      }
      return res * sgn;
    }

    public boolean isExhausted() {
      int value;
      while (isSpaceChar(value = peek()) && value != -1) {
        read();
      }
      return value == -1;
    }

    public String next() {
      return nextLine();
    }

    public SpaceCharFilter getFilter() {
      return filter;
    }

    public void setFilter(SpaceCharFilter filter) {
      this.filter = filter;
    }

    public interface SpaceCharFilter {
      public boolean isSpaceChar(int ch);
    }
    public int[] nextIntArray(int n){
      int[] array=new int[n];
      for(int i=0;i<n;++i)array[i]=nextInt();
      return array;
    }
    public int[] nextSortedIntArray(int n){
      int array[]=nextIntArray(n);
      Arrays.sort(array);
      return array;
    }
    public ArrayList<Integer> nextIntArrayList(int n){
      ArrayList<Integer> ar= new ArrayList<>();
      for(int i=0;i<n;i++)
        ar.add(nextInt());
      return ar;
    }
		public ArrayList<Long> nextLongArrayList(int n){
      ArrayList<Long> ar= new ArrayList<>();
      for(int i=0;i<n;i++)
        ar.add(nextLong());
      return ar;
    }

    public int[] nextSumIntArray(int n){
      int[] array=new int[n];
      array[0]=nextInt();
      for(int i=1;i<n;++i)array[i]=array[i-1]+nextInt();
      return array;
    }
    public long[] nextLongArray(int n){
      long[] array=new long[n];
      for(int i=0;i<n;++i)array[i]=nextLong();
      return array;
    }
    public long[] nextSumLongArray(int n){
      long[] array=new long[n];
      array[0]=nextInt();
      for(int i=1;i<n;++i)array[i]=array[i-1]+nextInt();
      return array;
    }
    public long[] nextSortedLongArray(int n){
      long array[]=nextLongArray(n);
      Arrays.sort(array);
      return array;
    }
    public int[][] nextIntMatrix(int n,int m){
      int[][] matrix=new int[n][m];
      for(int i=0;i<n;++i)
      for(int j=0;j<m;++j)
      matrix[i][j]=nextInt();
      return matrix;
    }

    public int[][] nextIntMatrix(int n){
      return nextIntMatrix(n,n);
    }

    public long[][] nextLongMatrix(int n,int m){
      long[][] matrix=new long[n][m];
      for(int i=0;i<n;++i)
      for(int j=0;j<m;++j)
      matrix[i][j]=nextLong();
      return matrix;
    }

    public long[][] nextLongMatrix(int n){
      return nextLongMatrix(n,n);
    }

    public char[][] nextCharMatrix(int n,int m){
      char[][] matrix=new char[n][m];
      for(int i=0;i<n;++i)
      matrix[i]=next().toCharArray();
      return matrix;
    }

    public char[][] nextCharMatrix(int n){
      return nextCharMatrix(n,n);
    }
  }

  static class OutputWriter {
    private final PrintWriter writer;

    public OutputWriter(OutputStream outputStream) {
      writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
    }

    public OutputWriter(Writer writer) {
      this.writer = new PrintWriter(writer);
    }

    // public void print(char[] array) {
    //     writer.print(array);
    // }

    public void print(Object... objects) {
      for (int i = 0; i < objects.length; i++) {
        if (i != 0) {
          writer.print(' ');
        }
        writer.print(objects[i]);
      }
    }

    public void print(int[] array) {
      for (int i = 0; i < array.length; i++) {
        if (i != 0) {
          writer.print(' ');
        }
        writer.print(array[i]);
      }
    }

    public void print(double[] array) {
      for (int i = 0; i < array.length; i++) {
        if (i != 0) {
          writer.print(' ');
        }
        writer.print(array[i]);
      }
    }

    public void print(long[] array) {
      for (int i = 0; i < array.length; i++) {
        if (i != 0) {
          writer.print(' ');
        }
        writer.print(array[i]);
      }
    }

    public void print(char[] array) {
      for (int i = 0; i < array.length; i++) {
        if (i != 0) {
          writer.print(' ');
        }
        writer.print(array[i]);
      }
    }

    public void print(String[] array) {
      for (int i = 0; i < array.length; i++) {
        if (i != 0) {
          writer.print(' ');
        }
        writer.print(array[i]);
      }
    }

    public void print(int[][] matrix){
      for(int i=0;i<matrix.length;++i){
        println(matrix[i]);
      }
    }

    public void print(double[][] matrix){
      for(int i=0;i<matrix.length;++i){
        println(matrix[i]);
      }
    }

    public void print(long[][] matrix){
      for(int i=0;i<matrix.length;++i){
        println(matrix[i]);
      }
    }

    public void print(char[][] matrix){
      for(int i=0;i<matrix.length;++i){
        println(matrix[i]);
      }
    }

    public void print(String[][] matrix){
      for(int i=0;i<matrix.length;++i){
        println(matrix[i]);
      }
    }

    public void println(int[] array) {
      print(array);
      writer.println();
    }

    public void println(double[] array) {
      print(array);
      writer.println();
    }

    public void println(long[] array) {
      print(array);
      writer.println();
    }

    // public void println(char[] array) {
    //     print(array);
    //     writer.println();
    // }

    public void println(String[] array) {
      print(array);
      writer.println();
    }

    public void println() {
      writer.println();
    }

    public void println(Object... objects) {
      print(objects);
      writer.println();
    }

    public void print(char i) {
      writer.print(i);
    }

    public void println(char i) {
      writer.println(i);
    }

    public void println(char[] array) {
      writer.println(array);
    }

    public void printf(String format, Object... objects) {
      writer.printf(format, objects);
    }

    public void close() {
      writer.close();
    }

    public void flush() {
      writer.flush();
    }

    public void print(long i) {
      writer.print(i);
    }

    public void println(long i) {
      writer.println(i);
    }

    public void print(int i) {
      writer.print(i);
    }

    public void println(int i) {
      writer.println(i);
    }

    public void separateLines(int[] array) {
      for (int i : array) {
        println(i);
      }
    }
  }
  static class NumberTheory{

      /**
       * Modular Arithmetic:
       *  1. (a+b)%c=(a%c+b%c)%c
       *  2. (a*b)%c=(a%c*b%c)%c
       *  3. (a-b)%c=(a%c-b%c+c)%c
       *  4. (a/b)%c=(a%c*(b^-1)%c)%c -- (b^-1 is multiplicative modulo inverse)
       */
      //Modular Addition
      public int modularAddition(int a,int b,int MOD){
          return (a%MOD+b%MOD)%MOD;
      }
      public long modularAddition(long a,long b,long MOD){
          return (a%MOD+b%MOD)%MOD;
      }
      //Modular Multiplication
      public int modularMultiplication(int a,int b,int MOD){
          return ((a%MOD)*(b%MOD))%MOD;
      }
      public long modularMultiplication(long a,long b,long MOD){
          return ((a%MOD)*(b%MOD))%MOD;
      }
      //Modular Subtraction
      public int modularSubtraction(int a,int b,int MOD){
          return (a%MOD-b%MOD+MOD)%MOD;
      }
      public long modularSubtraction(long a,long b,long MOD){
          return (a%MOD-b%MOD+MOD)%MOD;
      }

      /**
       * Binary Exponentiation
       */
      public int binaryExponentiation(int x,int n){
          if(n==0)return 1;
          else if(n%2==0)return binaryExponentiation(x*x,n/2);
          else return x*binaryExponentiation(x*x,(n-1)/2);
      }
      public long binaryExponentiation(long x,long n){
          long result=1;
          while(n>0){
              if(n%2==1)result*=x;
              x=x*x;
              n/=2;
          }
          return result;
      }

      /**
       * Modular Exponentiation
       */
      public int modularExponentiation(int x,int n,int MOD){
          if(n==0)return 1%MOD;
          else if(n%2==0)return modularExponentiation(modularMultiplication(x,x,MOD),n/2,MOD);
          else return modularMultiplication(x,modularExponentiation(modularMultiplication(x,x,MOD),(n-1)/2,MOD),MOD);
      }
      public long modularExponentiation(long x,long n,long MOD){
          long result=1;
          while(n>0){
              if(n%2==1)result=modularMultiplication(result,x,MOD);
              x=modularMultiplication(x,x,MOD);
              n/=2;
          }
          return result;
      }

      /**
       * Factorial of a number
       */
      public long factorials(long n){
          if(n==0)return 1;
          return n*factorials(n-1);
      }

      /**
       * Prime factors of a number
       */
      public ArrayList<Integer> distinctPrimeFactors(int n){
          ArrayList<Integer> factorials=new ArrayList<>();
          int limit=(int)Math.sqrt(n);
          if(n%2==0){
              factorials.add(2);
              while(n%2==0)n/=2;
          }
          for(int i=3;i<=limit;i+=2){
              if(n%i==0){
                  factorials.add(i);
                  while(n%i==0)n/=i;
              }
          }
          if(n>2)factorials.add(n);
          return factorials;
      }

      public ArrayList<Long> distinctPrimeFactors(long n){
          ArrayList<Long> factorials=new ArrayList<>();
          long limit=(long)Math.sqrt(n);
          if(n%2==0){
              factorials.add((long)2);
              while(n%2==0)n/=2;
          }
          for(long i=3;i<=limit;i+=2){
              if(n%i==0){
                  factorials.add(i);
                  while(n%i==0)n/=i;
              }
          }
          if(n>2)factorials.add(n);
          return factorials;
      }

      public ArrayList<Integer> primeFactors(int n){
          ArrayList<Integer> factorials=new ArrayList<>();
          int limit=(int)Math.sqrt(n);
          if(n%2==0){
              factorials.add(2);
              while(n%2==0)n/=2;
          }
          for(int i=3;i<=limit;i+=2){
              if(n%i==0){
                  factorials.add(i);
                  while(n%i==0)n/=i;
              }
          }
          if(n>2)factorials.add(n);
          return factorials;
      }

      public ArrayList<Long> primeFactors(long n){
          ArrayList<Long> factorials=new ArrayList<>();
          long limit=(long)Math.sqrt(n);
          if(n%2==0){
              factorials.add((long)2);
              while(n%2==0)n/=2;
          }
          for(long i=3;i<=limit;i+=2){
              if(n%i==0){
                  factorials.add(i);
                  while(n%i==0)n/=i;
              }
          }
          if(n>2)factorials.add(n);
          return factorials;
      }

      /**
       * Combination: nCr
       */
      //Naive version
      //(n,r)=(n-1,r-1)+(n-1,r) for r!=0 or r!=n
      //(n,0)=(n,n)=1
      public int binomialCoefficientRecursive(int n,int k){
          if(k==0 || k==n)return 1;//base case
          return binomialCoefficientRecursive(n-1,k-1)+binomialCoefficientRecursive(n-1,k);//recursion
      }

      //Dynamic Programming version(Uses bottom up approach to fill the table)
      //Time complexity: O(n*k)
      //Space complexity: O(n*k)
      public long binomialCoefficientIterative(int n,int k){
          long[][] C=new long[n+1][k+1];
          for(int i=0;i<=n;++i){
              for(int j=0;j<=Math.min(n,k);++j){
                  if(j==0 || j==i)C[i][j]=1;
                  else C[i][j]=C[i-1][j-1]+C[i-1][j];
              }
          }
          return C[n][k];
      }

      //Pascal's Triangle version(Space efficient program)
      //Time complexity: O(n*k)
      //Space complexity: O(k)
      public long nCr(int n,int r){
          int[] C=new int[r+1];
          C[0]=1;//nC0=1
          for(int i=1;i<=n;++i)
              for(int j=Math.min(i,r);j>0;--j)
                  C[j]=C[j]+C[j-1];
          return C[r];
      }

      /**
       * Catlan number:
       *  - Time complexity: O(n*n)
       *  - Auxiliary space: O(n)
       *
       *  NOTE: Time complexity could be reduced to O(n) but it is
       *        possible if and only if n is small or else there is
       *        a chance of getting an overflow. To decrease the time
       *        complexity to O(n) just remember nCr=nCn-r
       */
      public long catlanNumber(int n){
          long[] catlan=new long[n+1];
          catlan[0]=catlan[1]=1;
          for(int i=2;i<=n;++i)
              for(int j=0;j<i;++j)
                  catlan[i]+=catlan[j]*catlan[i-1-j];

          return catlan[n];
      }

      /**
       * Greatest Common Divisor(GCD)
       *  - It is also known as Highest Common Factor(HCF)
       *  - Time complexity: log(min(a,b))
       *  - Auxiliary Space: O(1)
       */
      public int gcd(int a,int b){
          if(b==0)return a;
          return gcd(b,a %b);
      }

      public long gcd(long a,long b){
          if(b==0)return a;
          return gcd(b,a%b);
      }

      /**
       * Extended Euclid's Algorithm:
       *  - ax+by=gcd(a,b)
       *  - Time complexity:
       *  -
       */


      /**
       * Least Common Multiple(LCM):
       *  - Time complexity: log(min(a,b))
       *  - Auxiliary Space: O(1)
       */
      public long lcm(long a,long b){
          return (a*b)/gcd(a,b);
      }

  }
}
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//                "I88I88I8m ,I8"   "I8""==mm ,mI8"
//        ___    ,mI8"    "8I8"      I8,  ,mI8I8"
//   .,mI8I8I8I8I88,      ,m8"      ,I8I8I8I888"
// "I8Im,       "I88,    ,8"      ,II8"     "88,
//    `"I8,        "I8, ,8"     ,I8"         "I8,
//       "I8m       "I888      ,I8"           "I8,
//         "8m        "I8      88"              "I8,
//          I8,        I8      88                 "I8,
//           88,       I8,     "I8                 "I8
//           "I8,      "I8,     "I8,                I8;.
//            "I8,      "I8,      "I8        .,mmmI8888888m,.
//              I8,      "I8,      I8,  .mI8I88"""". .. "I8888
//              "I8,      "I8      mI8I88"". . . . . .,m8"   "8
//               I8m,  __ ;I8   ,II88" . . . . .,;miI88"
//               "I88I8I88I88,,I88" . . . ,mmiiI8888"
//                ,I8". . ."I8I8". . . mi888888888"
//              ,I8 . . . .,I88I. . .i88888888888"
//             I8. . . .,mII88Ima. .i88888888888"
//            ,8"..,mI88I88I88I8Imi888888888888"
//            I8.,I8I"""        ""II88888888888
//           ;I8I8"                  ""I8888888
//           ""                         "I88888
//                                        "I888
//                                         "I88,
//                                          "I88
//                                           "88,
//                                            I88,              ______   __
//                           ______           "I88__        .mI88I88I88I88I88,
//                      .,mI88I88I88, ,mI88,   I88"""     ,mI8". . . . "I8,..8,
//                    ,I888' . . . "I88.\ "8,  I88      ,I8". . . .  / :;I8 \ 8,
//                  .mI8' . . .  / .:"I8.\ 88  "88,    ,8". . .  / .;mI8I8I8,\ 8
//                 ,I8'. . .  / . .:;,I8I8I888  I88   ,8". .  / .:mI8"'   "I8,:8
//                ,I8'. . . / . .:;,mI8"  `"I88 I88   I8. .  / .m8"         "I8I
//               ,I8 . .  / . .:;,mI8"      "I88888   88,.  / ,m8            "8'
//               I8'. .  / . .;,mI8"          "II888 ,I8I8,.,I8"
//               I8 . . / . .,mI8"              I8888888' """
//               `I8,.  / ;,mI8"                 II888
//                "I8I, /,mI8"                 __I888
//                  "I8888"                   """I88
//                    ""                         I88
//                                               I88__
//                                               I88"""
//                                               I88
//                                               I88
//                                             __I88
//                                            """I88
//                                               I88
//                                               I88
//                                               I88__
//                                               I88"""
//                                               I88
//                                        BITSY  ___  CHUCK
