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 long long INFLL = 0x3f3f3f3f3f3f3f3fLL;
inline long long read() {
  long long x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
const int maxn = 1e5 + 10;
int m, f[30];
char s[maxn];
int main() {
  cin >> m >> s + 1;
  int n = strlen(s + 1);
  for (char c = 'a'; c <= 'z'; c++) {
    int tmp = 0, flag = 1;
    for (int i = 1; i <= n; i++) {
      tmp++;
      if (tmp > m) {
        flag = 0;
        break;
      } else if (s[i] <= c)
        tmp = 0;
    }
    if (!flag) continue;
    tmp = 0;
    for (int i = 1; i <= n; i++) {
      tmp++;
      if (s[i] < c)
        f[s[i] - 'a']++, tmp = 0;
      else if (s[i] == c) {
        int j = 1, flag = 0;
        for (; j <= m - tmp; j++) {
          if (s[i + j] <= c) {
            flag = 1;
            break;
          }
        }
        if (!flag) f[s[i] - 'a']++, tmp = 0;
      }
    }
    break;
  }
  for (char c = 'a'; c <= 'z'; c++) {
    for (int i = 0; i < f[c - 'a']; i++) putchar(c);
  }
  puts("");
  return 0;
}
