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.Arrays;
import java.io.IOException;
import java.util.Random;
import java.io.InputStreamReader;
import java.util.StringTokenizer;
import java.io.BufferedReader;
import java.io.InputStream;

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

    static class TaskD {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int m = in.nextInt();
            String s = in.next();
            int n = s.length(), tot = 0;
            int[] min = new int[n - m + 1], cnt = new int[26];
            int cmin = 0;
            char[] a = s.toCharArray();
            StringBuilder sb = new StringBuilder();
            Sorts.sort(a);
            for (int i = 0; i < m; i++) {
                cnt[(int) (s.charAt(i)) - (int) 'a']++;
            }
            for (int j = 0; j < 26; j++) {
                if (cnt[j] > 0) {
                    min[0] = j;
                    break;
                }
            }
            for (int i = 1; i <= n - m; i++) {
                cnt[(int) (s.charAt(i - 1)) - (int) 'a']--;
                cnt[(int) (s.charAt(i + m - 1)) - (int) 'a']++;
                for (int j = 0; j < 26; j++) {
                    if (cnt[j] > 0) {
                        min[i] = j;
                        break;
                    }
                }
            }
            for (int i = 0; i <= n - m; i++) {
                cmin = Math.max(cmin, min[i]);
            }
            int j = 0;
            for (int i = 0; i <= n - m; i++) {
                if ((int) a[i] - (int) 'a' < cmin) {
                    sb.append(a[i]);
                } else {
                    while (j <= n - m && min[j] != cmin) {
                        j++;
                    }
                    if (j > n - m) {
                        break;
                    }
                    int k = j + m - 1;
                    if (k >= n) {
                        sb.append(a[i]);
                        break;
                    }
                    while ((int) s.charAt(k) - (int) 'a' != cmin) {
                        k--;
                    }
                    j = k + 1;
                    sb.append(a[i]);
                }
            }
            out.println(sb.toString());
        }

    }

    static class InputReader {
        private BufferedReader br;
        private StringTokenizer st;

        public InputReader(InputStream stream) {
            br = new BufferedReader(new InputStreamReader(stream), 32768);
            st = null;
        }

        public String next() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return st.nextToken();
        }

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

    }

    static class Sorts {
        private static void shuffle(char[] a) {
            int n = a.length;
            Random r = new Random();
            for (int i = 0; i < n; ++i) {
                char tmp = a[i];
                int pi = i + r.nextInt(n - i);
                a[i] = a[pi];
                a[pi] = tmp;
            }
        }

        public static void sort(char[] a) {
            shuffle(a);
            Arrays.sort(a);
        }

    }
}

