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 m, n;
char s[100000 + 100];
int t[100000 + 100];
int tt[100000 + 100];
int near;
int p[300];
int main() {
  scanf("%d", &m);
  scanf("%s", s + 1);
  n = strlen(s + 1);
  for (char c = 'a'; c <= 'z'; c++) {
    int ok = 1;
    for (char ch = 'a'; ch <= 'z'; ch++) p[ch] = 0;
    for (int i = 1; i <= n; i++) tt[i] = t[i];
    for (int i = 1; i <= n; i++) {
      p[s[i]] = i;
      if (i >= m and t[i] == 0 and p[c] <= i - m) ok = 0;
      if (i >= m and p[c] > i - m) t[i] = 1;
    }
    if (ok == 0) {
      for (int i = 1; i <= n; i++)
        if (s[i] == c) printf("%c", c);
      continue;
    }
    for (char ch = 'a'; ch <= 'z'; ch++) p[ch] = 0;
    for (int i = 1; i <= n; i++) {
      p[s[i]] = i;
      if (i >= m and tt[i] == 0 and (near == 0 or near <= i - m))
        printf("%c", c), near = p[c];
    }
    break;
  }
  return 0;
}
