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 cmd(char x, char y) { return x < y; }
int main() {
  int n;
  char a[210000];
  scanf("%d%s", &n, a);
  int len = strlen(a);
  if (n > len) {
    int Max = 10000;
    for (int i = 0; i < len; i++) {
      if (Max > a[i]) Max = a[i];
    }
    printf("%c", Max);
    return 0;
  }
  int MAX = -10000;
  for (int i = 0; i < len; i++) {
    int ss = i + n;
    if (ss > len) break;
    int Max = 10000, zz;
    for (; i < ss; i++) {
      if (Max > a[i]) {
        Max = a[i];
        zz = i;
      }
    }
    if (MAX < Max) MAX = Max;
    i = zz;
  }
  char cnt[210000];
  int cot = 0;
  for (int i = 0; i < len; i++) {
    if (a[i] < MAX) {
      cnt[cot++] = a[i];
      continue;
    }
    int ss = i + n;
    if (ss > len) {
      for (i; i < len; i++) {
        if (a[i] < MAX) {
          cnt[cot++] = a[i];
        }
      }
      break;
    }
    int Max = 100000, zz;
    for (i; i < ss; i++) {
      if (a[i] < MAX) {
        cnt[cot++] = a[i];
        break;
      }
      if (Max >= a[i]) {
        Max = a[i];
        zz = i;
      }
    }
    if (i == ss) {
      i = zz;
      cnt[cot++] = Max;
    }
  }
  cnt[cot] = '\0';
  sort(cnt, cnt + cot, cmd);
  printf("%s", cnt);
  return 0;
}
