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;
string second;
int m, n;
string ans = "";
int dp[100011][26];
int inc[100011];
int main() {
  cin >> m;
  cin >> second;
  char cp = 'a';
  cp--;
  int n = second.size();
  for (char c = 'a'; c <= 'z'; c++) {
    int cnt = 0;
    for (int i = 0; i < m - 1; i++) {
      cnt += (second[i] <= c);
    }
    bool ok = 1;
    for (int i = m - 1; i < n; i++) {
      cnt += (second[i] <= c);
      if (cnt == 0) {
        ok = 0;
        break;
      }
      cnt -= (second[i - m + 1] <= c);
    }
    if (!ok) continue;
    cp = c;
    break;
  }
  for (int i = 0; i < second.size(); i++) {
    for (int j = 0; j < 26; j++) {
      dp[i + 1][j] = dp[i][j];
    }
    dp[i + 1][second[i] - 'a'] = i + 1;
  }
  int cnt = 0;
  for (int i = 0; i < m - 1; i++) {
    cnt += (second[i] < cp);
  }
  for (int i = m - 1; i < n; i++) {
    cnt += (second[i] < cp);
    if (cnt == 0) {
      int j = dp[i + 1][cp - 'a'] - 1;
      inc[j] = 1;
      cnt++;
    }
    cnt -= (second[i - m + 1] < cp);
    cnt -= inc[i - m + 1];
  }
  for (int i = 0; i < n; i++) {
    if (inc[i]) ans += second[i];
    if (second[i] < cp) ans += second[i];
  }
  sort(ans.begin(), ans.end());
  cout << ans;
}
