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".
#include <bits/stdc++.h>
using namespace std;
int sum[100005], s[100005];
char A[100005], B[100005], C[100005];
int main() {
  int m, t = 0;
  scanf("%d", &m);
  scanf("%s", A + 1);
  int n = strlen(A + 1);
  for (int x = 0; x < 26; x++) {
    char c = x + 'a';
    bool f = 1;
    sum[0] = 0;
    for (int i = 1; i <= n; i++) {
      if (A[i] <= c) {
        sum[i] = sum[i - 1] + 1;
      } else
        sum[i] = sum[i - 1];
    }
    for (int i = 1; i <= n - m + 1; i++) {
      if (sum[i + m - 1] - sum[i - 1] <= 0) {
        f = 0;
        break;
      }
    }
    if (!f) continue;
    if (f) {
      for (int i = 1; i <= n; i++) {
        if (A[i] < c) {
          s[i] = s[i - 1] + 1;
        } else
          s[i] = s[i - 1];
      }
      for (int i = 1; i <= n; i++) {
        if (s[i] - s[i - 1] == 0) continue;
        B[i] = 1;
      }
      int pre = 0;
      for (int i = 1; i <= n; i++) {
        if (B[i])
          pre = i;
        else {
          if (i - pre >= m) {
            for (int j = i; j >= i - m && j >= 0; j--) {
              if (A[j] == c) {
                B[j] = 1;
                pre = j;
                break;
              }
            }
          }
        }
      }
      for (int i = 1; i <= n; i++) {
        if (B[i]) {
          C[++t] = A[i];
        }
      }
      sort(C + 1, C + t + 1);
      for (int i = 1; i <= t; i++) {
        printf("%c", C[i]);
      }
      puts("");
      break;
    }
  }
  return 0;
}
