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;
char S[(long long)1e5 + 2];
int main() {
  int N, M;
  scanf("%d ", &M);
  fgets(S, (long long)1e5 + 2, stdin);
  N = strlen(S) - 1;
  S[N] = 0;
  int k = 0;
  for (k = 1; k <= 26; k <<= 1)
    ;
  k >>= 1;
  int i = -1;
  for (i = -1; k; k >>= 1)
    if (i + k < 26) {
      char worst = 'a' + i + k;
      int last = -1;
      int j = 0;
      for (j = 0; j < N; j++) {
        if (S[j] <= worst) last = j;
        if (j - last >= M) break;
      }
      if (j != N) i += k;
    }
  char worst = 'a' + i + 1;
  vector<char> ret;
  int last = -1;
  int j = 0;
  int last_worst = -1;
  for (j = 0; j < N; j++) {
    if (S[j] < worst) {
      last = j;
      ret.push_back(S[j]);
    }
    if (S[j] == worst) {
      last_worst = j;
    }
    if (j - last >= M) {
      last = last_worst;
      ret.push_back(worst);
    }
  }
  sort(ret.begin(), ret.end());
  for (auto i : ret) printf("%c", i);
  printf("\n");
  return 0;
}
