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 num[1100];
char st[101000];
int m, n;
int process(char ch) {
  int ans = 0;
  int pch = 0x3f3f3f3f;
  int p = 0x3f3f3f3f;
  int j = n - 1;
  for (int i = n; i >= m;) {
    for (; j >= i - m; j--) {
      if (st[j] == ch) pch = j;
      if (st[j] < ch) p = j;
    }
    if (p < i) {
      i = p;
      continue;
    }
    if (pch < i) {
      ans++;
      i = pch;
      continue;
    }
    return -1;
  }
  return ans;
}
int main() {
  scanf("%d", &m);
  scanf("%s", st);
  n = strlen(st);
  memset(num, 0, sizeof(num));
  for (int i = 0; i < n; i++) {
    num[st[i]]++;
  }
  for (int ch = 'a'; ch <= 'z'; ch++) {
    int ans = process(ch);
    if (ans == -1) continue;
    for (int c = 'a'; c < ch; c++) {
      for (int i = 1; i <= num[c]; i++) putchar(c);
    }
    for (int i = 1; i <= ans; i++) putchar(ch);
    break;
  }
  printf("\n");
  return 0;
}
