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;
vector<bool> arr;
int main() {
  int m;
  scanf("%d", &m);
  string str;
  cin >> str;
  int n = str.length();
  int s = n - m + 1;
  arr.resize(s);
  string jaw = "";
  for (int c = 0; c < 26; ++c) {
    bool flag = true;
    int count = 0;
    int maxi = -1;
    for (int i = 0; i < s; ++i) {
      if (arr[i]) continue;
      if (maxi >= i) {
        arr[i] = true;
        continue;
      }
      maxi = -1;
      for (int j = i + m - 1; j >= i; --j) {
        if (str[j] == c + 'a') {
          maxi = j;
          arr[i] = true;
          ++count;
          break;
        }
      }
      if (maxi == -1) {
        flag = false;
      }
    }
    if (flag) {
      for (int i = 0; i < count; ++i) {
        jaw += c + 'a';
      }
      printf("%s\n", jaw.c_str());
      return 0;
    }
    for (int i = 0; i < n; ++i) {
      if (str[i] == c + 'a') jaw += c + 'a';
    }
  }
  printf("%s\n", jaw.c_str());
}
