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 c[300];
int ct[300];
int main() {
  set<int> st;
  int m;
  for (int i = 0; i < 300; i++) {
    c[i] = -1;
  }
  cin >> m;
  string s;
  cin >> s;
  int len = s.size();
  for (int i = 0; i < len; i++) {
    ct[s[i]]++;
  }
  for (int i = 0; i < m; i++) {
    c[s[i]] = i;
  }
  int mx = -1;
  for (int j = 'a'; j <= 'z'; j++) {
    if (c[j] != -1) {
      mx = max(j, mx);
      break;
    }
  }
  for (int i = 1; i < len - m + 1; i++) {
    if (c[s[i - 1]] < i) {
      c[s[i - 1]] = -1;
    }
    c[s[i + m - 1]] = i + m - 1;
    for (int j = 'a'; j <= 'z'; j++) {
      if (c[j] != -1) {
        mx = max(j, mx);
        break;
      }
    }
  }
  for (int i = 0; i < 300; i++) {
    c[i] = -1;
  }
  int prev = -1;
  for (int i = 0; i < m; i++) {
    c[s[i]] = i;
  }
  for (int j = 'a'; j <= 'z'; j++) {
    if (c[j] != -1) {
      if (j != mx) {
        break;
      }
      prev = c[j];
      st.insert(prev);
      break;
    }
  }
  for (int i = 1; i < len - m + 1; i++) {
    if (c[s[i - 1]] < i) {
      c[s[i - 1]] = -1;
    }
    c[s[i + m - 1]] = i + m - 1;
    for (int j = 'a'; j <= 'z'; j++) {
      if (c[j] != -1) {
        if (j != mx) {
          break;
        }
        if (prev < i) {
          prev = c[j];
          st.insert(prev);
          break;
        }
      }
    }
  }
  string ans;
  for (int i = 'a'; i <= 'z'; i++) {
    if (i < mx) {
      for (int j = 0; j < ct[i]; j++) {
        ans += i;
      }
    }
  }
  for (int i = 0; i < st.size(); i++) {
    ans += mx;
  }
  cout << ans << endl;
  return 0;
}
