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 INF = 0x3f3f3f3f;
const double eps = 1e-8;
const long long MOD = 1000000007;
const long long MAXN = 100001;
int main() {
  int i, j, k;
  int n, m, T;
  cin >> n;
  char a[MAXN];
  int cnt[30];
  for (i = 0; i < 30; i++) {
    cnt[i] = 0;
  }
  scanf("%s", a);
  int len = strlen(a);
  if (len <= n) {
    int mn = 'z';
    for (j = 0; j < len; j++) {
      if (a[j] <= mn) {
        mn = a[j];
      }
    }
    printf("%c\n", mn);
    return 0;
  }
  int mx = 0;
  for (i = 0; i < len - n; i++) {
    int mn = 'z';
    int index = -1;
    for (j = i; j < i + n; j++) {
      if (a[j] <= mn) {
        mn = a[j];
        index = j;
      }
    }
    if (index != -1) {
      int k = mn - 'a';
      cnt[k]++;
      i = index;
      if (mx < k) {
        mx = k;
      }
      a[index] = ' ';
    }
  }
  for (i = 0; i < len; i++) {
    if (a[i] != ' ') {
      int k = a[i] - 'a';
      if (k < mx) {
        cnt[k]++;
      }
    }
  }
  for (i = 0; i < 26; i++) {
    while (cnt[i]--) {
      printf("%c", 'a' + i);
    }
  }
  printf("\n");
  return 0;
}
