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;
const int maxn = 100000 + 7;
char sou[maxn];
int n, s[30], a[maxn];
int main() {
  while (~scanf("%d", &n)) {
    memset(a, 0, sizeof(a));
    string x;
    cin >> x;
    int len = x.length();
    for (int i = 0; i < len; i++) {
      a[i + 1] = x[i] - 'a';
      s[a[i + 1]]++;
    }
    int sum = 0, i, j;
    for (i = 0; i <= 25; i++) {
      int d = 0;
      for (j = 1; j <= len; j++) {
        if (a[j] <= i)
          d = 0;
        else
          d++;
        if (d == n) break;
      }
      if (d != n) {
        d = 0;
        int la = 0;
        for (j = 1; j <= len; j++) {
          if (a[j] < i)
            d = 0;
          else {
            d++;
            if (a[j] == i) la = j;
          }
          if (d == n) {
            d = j - la;
            sum++;
          }
        }
        break;
      }
    }
    for (int x = 0; x < i; x++) {
      for (int l = 0; l < s[x]; l++) printf("%c", x + 'a');
    }
    for (j = 1; j <= sum; j++) printf("%c", i + 'a');
    printf("\n");
  }
  return 0;
}
