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 n, l;
char z[120000];
int a[30];
int check(int x) {
  int i, j, last = -1;
  for (i = 1; i <= n; i++)
    if (z[i] <= 'a' + x - 1) last = i;
  if (last == -1) return 0;
  for (i = last + 1; i <= l - n + 1; i++) {
    if (z[i] <= 'a' + x - 1) last = i;
    if (i > last) {
      for (j = i + 1; j <= i + n - 1 && j <= l; j++) {
        if (z[j] <= 'a' + x - 1) last = j;
      }
      if (i > last) return 0;
    }
  }
  return 1;
}
int solve(int x) {
  int i, j, last = -1, sum, lp;
  sum = 0;
  lp = -1;
  x--;
  for (i = 1; i <= n; i++) {
    if (z[i] <= 'a' + x - 1) last = i;
    if (z[i] == 'a' + x) lp = i;
  }
  if (last == -1) last = lp, sum++;
  for (i = last + 1; i <= l - n + 1; i++) {
    if (z[i] <= 'a' + x - 1) last = i;
    if (z[i] == 'a' + x) lp = i;
    if (i > last) {
      for (j = i + 1; j <= i + n - 1 && j <= l; j++) {
        if (z[j] <= 'a' + x - 1) last = j;
        if (z[j] == 'a' + x) lp = j;
      }
      if (i > last) {
        sum++;
        last = lp;
      }
    }
  }
  return sum;
}
void work() {
  int i, j, ans, ansi;
  scanf("%d", &n);
  scanf("%s", z + 1);
  l = strlen(z + 1);
  for (i = 1; i <= 26; i++) {
    if (check(i) == 1) {
      ans = solve(i);
      ansi = i;
      break;
    }
  }
  for (i = 1; i <= l; i++) {
    a[z[i] - 'a' + 1]++;
  }
  for (i = 1; i < ansi; i++)
    for (j = 1; j <= a[i]; j++) printf("%c", 'a' + i - 1);
  for (i = 1; i <= ans; i++) printf("%c", 'a' + ansi - 1);
  printf("\n");
}
int main() {
  work();
  return 0;
}
