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 ch[100005], ans[100005];
int n, m, s[100005][33];
bool check(int ch) {
  for (int i = 1; i + m - 1 <= n; i++) {
    bool flag = 1;
    for (int j = 1; j <= ch; j++) {
      if (s[i + m - 1][j] - s[i - 1][j] > 0) {
        flag = 0;
        break;
      }
    }
    if (flag) return 0;
  }
  return 1;
}
int main() {
  cin >> m >> (ch + 1);
  n = strlen(ch + 1);
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= 26; j++) s[i][j] = s[i - 1][j];
    s[i][ch[i] - 'a' + 1]++;
  }
  int l = 1, r = 26, find;
  while (l <= r) {
    int mid = (l + r) / 2;
    if (check(mid)) {
      r = mid - 1;
      find = mid;
    } else
      l = mid + 1;
  }
  int sum = s[n][find];
  for (int i = 1; i + m - 1 <= n; i++) {
    int mi = INT_MAX, k = 0;
    for (int j = 0; j < m; j++) {
      if (ch[i + j] == ' ') {
        k = 0;
        break;
      }
      if (ch[i + j] <= mi) {
        k = i + j;
        mi = ch[i + j];
      }
    }
    ch[k] = ' ';
  }
  for (int i = 1; i <= n; i++) {
    if (ch[i] == find + 'a' - 1) sum--;
  }
  for (int i = 1; i < find; i++) {
    for (int j = 1; j <= s[n][i]; j++) cout << char(i + 'a' - 1);
  }
  for (int i = 1; i <= sum; i++) cout << char(find + 'a' - 1);
  return 0;
}
