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;
int m, len;
char s[N];
int cnt[256];
int check(char c) {
  int ret = 0;
  int last = -1, lastc = -1;
  for (int i = 0; i < len; i++) {
    if (s[i] < c)
      last = i;
    else if (s[i] == c) {
      if (i - last > m) {
        if (lastc != -1) {
          ret++;
          last = max(lastc, last);
          lastc = -1;
        }
        if (i - last > m) return -1;
      }
      if (i - last == m) {
        last = i;
        ret++;
        lastc = -1;
      } else
        lastc = i;
    } else {
      if (i - last >= m) {
        if (lastc != -1) {
          ret++;
          last = max(lastc, last);
          lastc = -1;
        }
        if (i - last >= m) return -1;
      }
    }
  }
  assert(ret > 0);
  return ret;
}
int main() {
  scanf("%d", &m);
  scanf("%s", s);
  len = strlen(s);
  for (int i = 0; i < len; i++) cnt[s[i]]++;
  for (char c = 'a'; c <= 'z'; c++)
    if (cnt[c]) {
      int t = check(c);
      if (t != -1) {
        for (char cc = 'a'; cc < c; cc++) {
          for (int i = 0; i < cnt[cc]; i++) putchar(cc);
        }
        while (t--) putchar(c);
        return 0;
      }
    }
  return 0;
}
