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 main() {
  int m, n;
  string s;
  cin >> m >> s;
  n = s.size();
  vector<int> vi(26, 0);
  for (int i = 0; i < n; ++i) {
    s[i] -= 'a';
    ++vi[s[i]];
  }
  for (int i = 0; i < 26; ++i) {
    int tcnt = 0;
    map<int, int> mp;
    for (int j = 0; j < m; ++j) {
      if (s[j] <= i) {
        mp[s[j]] = j;
      }
    }
    int mx = 0;
    for (int j = 0; j + m - 1 < n; ++j) {
      if (mp.size() == 0) {
        tcnt = -1;
        break;
      }
      if (j >= mx) {
        if (mp.begin()->first == i) {
          ++tcnt;
        }
        mx = mp.begin()->second + 1;
      }
      if (mp.count(s[j]) && mp[s[j]] == j) {
        mp.erase(s[j]);
      }
      if (j + m < n && s[j + m] <= i) {
        mp[s[j + m]] = j + m;
      }
    }
    if (tcnt != -1) {
      while (tcnt--) {
        cout << (char)('a' + i);
      }
      break;
    } else {
      while (vi[i]--) {
        cout << (char)('a' + i);
      }
    }
  }
  return 0;
}
