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;
int x;
char s[100005];
bool flag[500];
int cnt[500];
vector<char> f;
int main() {
  scanf("%d", &x);
  scanf("%s", s);
  int len = strlen(s);
  for (int i = 0; i < len; i++) cnt[s[i]]++;
  for (int i = 'a'; i <= 'z'; i++) {
    if (cnt[i] == 0) continue;
    flag[i] = 1;
    int pre = -1;
    bool tag = 0;
    f.push_back(char(i));
    for (int j = 0; j < len; j++) {
      if (flag[s[j]]) {
        pre = j;
        continue;
      }
      int y = j - pre;
      if (y >= x) {
        tag = 1;
        break;
      }
    }
    if (tag)
      continue;
    else {
      cnt[i] = 0;
      flag[i] = 0;
      int pos = -1;
      int pre = -1;
      for (int j = 0; j < len; j++) {
        if (s[j] == i) {
          pos = max(pos, j);
        }
        if (flag[s[j]]) {
          pre = j;
          continue;
        }
        int y = j - pre;
        if (y >= x) {
          pre = pos;
          cnt[i]++;
        }
      }
      break;
    }
  }
  string ans = "";
  int p = f.size();
  for (int i = 0; i < p; i++) {
    for (int j = 1; j <= cnt[f[i]]; j++) ans += f[i];
  }
  cout << ans << endl;
  return 0;
}
