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;
inline long long sqr(long long x) { return x * x; }
const int N = 1e5 + 5;
int n, m, cnt[26];
char s[N];
int main() {
  scanf("%d%s", &m, s + 1);
  n = strlen(s + 1);
  for (int i = (1), _b = (n); i <= _b; ++i) ++cnt[s[i] - 'a'];
  for (int i = 0, _a = (26); i < _a; ++i) {
    int cnt2 = 0, last1 = 0, last2 = 0;
    for (int j = (1), _b = (n); j <= _b; ++j) {
      if (s[j] - 'a' < i)
        last1 = j;
      else if (s[j] - 'a' == i)
        last2 = j;
      if (j - last1 == m) {
        if (last2 <= last1) {
          cnt2 = -1;
          break;
        }
        ++cnt2;
        last1 = last2;
      }
    }
    if (cnt2 == -1)
      for (int j = (1), _b = (cnt[i]); j <= _b; ++j)
        printf("%c", (char)(i + 'a'));
    else {
      for (int j = (1), _b = (cnt2); j <= _b; ++j)
        printf("%c", (char)(i + 'a'));
      break;
    }
  }
  return 0;
}
