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 N = 1e5 + 10;
char s[N];
int x[300], m;
int ok(int l, int r, char c) {
  int R = l + m;
  while (R < r) {
    int f = 0;
    for (int i = R; i > R - m; i--) {
      if (s[i] == c) {
        f = 1;
        R = i + m;
        x[c]++;
        s[i] = '0';
        break;
      }
    }
    if (!f) return 0;
  }
  return 1;
}
int main() {
  int f = 0, len;
  scanf("%d %s", &m, s + 1);
  s[0] = '0';
  len = strlen(s);
  s[len] = '0';
  memset(x, 0, sizeof(x));
  for (char c = 'a'; c <= 'z'; c++) {
    f = 1;
    if (c > 'a')
      for (int i = 1; i < len; i++)
        if (s[i] == c - 1) s[i] = '0', x[c - 1]++;
    for (int i = 1, p = 0; i <= len; i++) {
      if (s[i] == '0') {
        if (i - p > 0 && !ok(p, i, c)) {
          f = 0;
          break;
        }
        p = i;
      }
    }
    if (f) break;
  }
  for (char c = 'a'; c <= 'z'; c++) {
    while (x[c]--) putchar(c);
  }
  printf("\n");
  return 0;
}
