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>
double eps = 1e-9;
using namespace std;
char ch[100005], mud[200];
int m, cnt[100005], sum[30][100005];
bool used[100005];
bool check(int l, int r, int x) { return sum[x][r] - sum[x][l - 1] > 0; }
int bin_search(int l, int r, int x) {
  while (r - l > 1) {
    int mid = (l + r) / 2;
    if (check(mid + 1, r, x))
      l = mid + 1;
    else
      r = mid;
  }
  if (l > r) swap(l, r);
  if (check(r, r, x)) return r;
  if (check(l, l, x)) return l;
  return -1;
}
int main() {
  cin >> m;
  gets(mud);
  gets(ch);
  int n = strlen(ch);
  for (int i = n; i >= 1; i--) ch[i] = ch[i - 1];
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j < 26; j++) sum[j][i] = sum[j][i - 1];
    sum[ch[i] - 'a'][i]++;
  }
  for (int j = 0; j < 26; j++) {
    bool found = 0;
    for (int i = 1; i <= n - m + 1; i++) {
      if (!used[i]) {
        int idx = bin_search(i, i + m - 1, j);
        if (idx == -1) {
          found = 1;
          break;
        } else {
          cnt[j]++;
          for (int k = i; k <= idx; k++) used[k] = 1;
          i = idx;
        }
      }
    }
    if (found) {
      cnt[j] = sum[j][n];
      for (int i = 1; i <= n - m + 1; i++) {
        if (sum[j][i + m - 1] - sum[j][i - 1] > 0) used[i] = 1;
      }
    } else
      break;
  }
  for (int j = 0; j < 26; j++) {
    for (int i = 1; i <= cnt[j]; i++) printf("%c", (char)(j + (int)'a'));
  }
  puts("");
}
