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[300005];
int minn[300005][20], ans[300005];
int a[30];
int p[300005];
int main() {
  int n;
  scanf("%d", &n);
  cin >> s + 1;
  int len = strlen(s + 1);
  memset(minn, 0x3f, sizeof(minn));
  for (int i = 1; i <= len; i++) {
    a[s[i] - 'a']++;
    minn[i][0] = s[i];
  }
  for (int i = 1; i <= 18; i++) {
    for (int j = 1; j <= len; j++)
      minn[j][i] = min(minn[j][i - 1], minn[j + (1 << (i - 1))][i - 1]);
  }
  memset(ans, 0x3f, sizeof(ans));
  int T = 0;
  while (1 << (T + 1) <= n) T++;
  int maxn = -1;
  for (int i = 1; i + n - 1 <= len; i++) {
    int l = i, r = i + n;
    int t = T;
    while (l < r) {
      if (l + (1 << t) <= r) {
        ans[i] = min(ans[i], minn[l][t]);
        l += (1 << t);
      }
      t--;
    }
    maxn = max(maxn, ans[i] - 'a');
  }
  for (int i = 0; i < maxn; i++) {
    for (int j = 1; j <= a[i]; j++) putchar(i + 'a');
  }
  int cnt = 0, sum = 0;
  for (int i = 1; i + n - 1 <= len; i++) {
    if (i <= cnt) continue;
    if (ans[i] - 'a' == maxn) {
      int j = i + n - 1;
      while (s[j] != maxn + 'a') j--;
      cnt = j;
      sum++;
    }
  }
  for (int i = 1; i <= sum; i++) putchar(maxn + 'a');
  return 0;
}
