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.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.SortedSet;
import java.util.Set;
import java.io.IOException;
import java.util.TreeSet;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Denis Nedelyaev
 */
public class Main {
    public static void main(String[] args) throws Exception {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        FastScanner in = new FastScanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskD solver = new TaskD(in, out);
        solver.solve(1);
        out.close();
    }

    static class TaskD {
        private final FastScanner in;
        private final PrintWriter out;

        public TaskD(FastScanner in, PrintWriter out) {
            this.in = in;
            this.out = out;
        }

        public void solve(int testNumber) throws IOException {
            int m = in.nextInt();
            char[] s = in.next().toCharArray();
            int[] countTotal = new int['z' + 1];
            int[] countUsed = new int['z' + 1];

            SortedSet<Integer> current = new TreeSet<>((a, b) -> s[a] == s[b] ? b - a : s[a] - s[b]);
            int last = -1;
            int max = -1;
            for (int i = 0; i < s.length; i++) {
                countTotal[s[i]]++;
                if (i >= m) {
                    current.remove(i - m);
                }
                current.add(i);
                if (i - m + 1 > last) {
                    last = current.first();
                    int c = s[last];
                    max = Math.max(max, c);
                    countUsed[c]++;
                }
            }

            for (int i = 'a'; i < max; i++) {
                for (int j = 0; j < countTotal[i]; j++) {
                    out.print((char) i);
                }
            }

            for (int j = 0; j < countUsed[max]; j++) {
                out.print((char) max);
            }

            out.println();
        }

    }

    static class FastScanner {
        private final static int BUFFER_SIZE = 4096;
        private final InputStream in;
        private final StringBuilder sb = new StringBuilder();
        private byte[] buffer = new byte[BUFFER_SIZE];
        private int pos = 0;
        private int size;

        public FastScanner(InputStream inputStream) throws IOException {
            in = inputStream;
            size = 0;
        }

        public String next() {
            int c = skipWhitespace();
            if (c == -1) {
                return null;
            }

            sb.setLength(0);

            do {
                sb.append((char) c);
                c = read();
            } while (c > ' ');

            return sb.toString();
        }

        public int nextInt() {
            int c = skipWhitespace();

            int sign = -1;
            if (c == '-') {
                sign = 1;
                c = read();
            }

            int ans = 0;

            while (c > ' ') {
                ans *= 10;
                ans -= c - '0';
                c = read();
            }

            return sign * ans;
        }

        private int skipWhitespace() {
            while (true) {
                int c = read();
                if (c > ' ' || c == -1) {
                    return c;
                }
            }
        }

        private int read() {
            if (pos >= size) {
                try {
                    size = in.read(buffer, 0, BUFFER_SIZE);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
                if (size <= 0) {
                    return -1;
                }
                pos = 0;
            }
            return buffer[pos++];
        }

    }
}

