You are given a string s, consisting of lowercase English letters, and the integer m.

One should choose some symbols from the given string so that any contiguous subsegment of length m has at least one selected symbol. Note that here we choose positions of symbols, not the symbols themselves.

Then one uses the chosen symbols to form a new string. All symbols from the chosen position should be used, but we are allowed to rearrange them in any order.

Formally, we choose a subsequence of indices 1 ≤ i1 < i2 < ... < it ≤ |s|. The selected sequence must meet the following condition: for every j such that 1 ≤ j ≤ |s| - m + 1, there must be at least one selected index that belongs to the segment [j, j + m - 1], i.e. there should exist a k from 1 to t, such that j ≤ ik ≤ j + m - 1.

Then we take any permutation p of the selected indices and form a new string sip1sip2... sipt.

Find the lexicographically smallest string, that can be obtained using this procedure.

Input

The first line of the input contains a single integer m (1 ≤ m ≤ 100 000).

The second line contains the string s consisting of lowercase English letters. It is guaranteed that this string is non-empty and its length doesn't exceed 100 000. It is also guaranteed that the number m doesn't exceed the length of the string s.

Output

Print the single line containing the lexicographically smallest string, that can be obtained using the procedure described above.

Examples

Input

3
cbabc


Output

a


Input

2
abcab


Output

aab


Input

3
bcabcbaccba


Output

aaabb

Note

In the first sample, one can choose the subsequence {3} and form a string "a".

In the second sample, one can choose the subsequence {1, 2, 4} (symbols on this positions are 'a', 'b' and 'a') and rearrange the chosen symbols to form a string "aab".
import java.io.*;
import java.util.*;

public class D {
    public static void solution(BufferedReader reader, PrintWriter out)
            throws IOException {
        In in = new In(reader);
        int m = in.nextInt();
        char[] s = in.next().toCharArray();
        int n = s.length;
        char c = 'a';
        loop: for (;; c++) {
            int pre = -1;
            for (int i = 0; i < n; i++)
                if (s[i] <= c)
                    pre = i;
                else if (i - pre >= m)
                    continue loop;
            break;
        }

        int[] cnt = new int[26];
        int pre = -1, cur = -1;
        for (int i = 0; i < n; i++) {
            if (s[i] < c) {
                pre = i;
                cnt[s[i] - 'a']++;
            }
            else if (s[i] == c)
                cur = i;
            if (i - pre == m) {
                pre = cur;
                cnt[c - 'a']++;
            }
        }
        StringBuffer rst = new StringBuffer();
        for (char ch = 'a'; ch <= c; ch++)
            for (int i = 0; i < cnt[ch - 'a']; i++)
                rst.append(ch);
        out.println(rst.toString());
    }

    protected static class RMQ {

        private int[] M; // M[0] is never used
        private char[] A;
        private int n;

        // O(n)
        public RMQ(char[] A) {
            this.A = A;
            n = A.length;
            M = new int[n << 1];
            for (int i = 0; i < n; i++)
                M[i + n] = i;
            for (int i = n - 1; i > 0; i--) {
                if (A[M[i << 1]] < A[M[i << 1 | 1]])
                    M[i] = M[i << 1];
                else
                    M[i] = M[i << 1 | 1];
            }
        }

        // [i, j) O(logn)
        public int rmq(int i, int j) {
            int min = i;
            for (i += n, j += n; i < j; i >>= 1, j >>= 1) {
                if ((i & 1) > 0) {
                    if (A[M[i]] < A[min])
                        min = M[i];
                    i++;
                }
                if ((j & 1) > 0) {
                    if (A[M[--j]] < A[min])
                        min = M[j];
                }
            }
            return min;
        }

    }

    public static void main(String[] args) throws Exception {
        BufferedReader reader = new BufferedReader(
                new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(
                new BufferedWriter(new OutputStreamWriter(System.out)));
        solution(reader, out);
        out.close();
    }

    protected static class In {
        private BufferedReader reader;
        private StringTokenizer tokenizer = new StringTokenizer("");

        public In(BufferedReader reader) {
            this.reader = reader;
        }

        public String next() throws IOException {
            while (!tokenizer.hasMoreTokens())
                tokenizer = new StringTokenizer(reader.readLine());
            return tokenizer.nextToken();
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

        public double nextDouble() throws IOException {
            return Double.parseDouble(next());
        }

        public long nextLong() throws IOException {
            return Long.parseLong(next());
        }
    }
}
