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;
const long long mod = 1000000007;
long long powmod(long long a, long long b) {
  long long res = 1;
  a %= mod;
  assert(b >= 0);
  for (; b; b >>= 1) {
    if (b & 1) res = res * a % mod;
    a = a * a % mod;
  }
  return res;
}
const int N = 101000;
char s[N];
int m, v[30], n;
int gao(int c) {
  int pre = -1, cand = -1, ret = 0;
  for (int i = 0; i < n; i++) {
    if (s[i] < 'a' + c) pre = i, cand = i;
    if (s[i] == 'a' + c) cand = i;
    if (i - pre == m) {
      if (cand > pre) {
        ret++;
        pre = cand;
      } else
        return -1;
    }
  }
  return ret;
}
int main() {
  scanf("%d", &m);
  scanf("%s", s);
  n = strlen(s);
  for (int i = 0; i < n; i++) v[s[i] - 'a']++;
  for (int i = 0; i < 26; i++) {
    int c = gao(i);
    if (c != -1) {
      for (int j = 0; j < i; j++)
        for (int k = 0; k < v[j]; k++) putchar('a' + j);
      for (int k = 0; k < c; k++) putchar('a' + i);
      puts("");
      return 0;
    }
  }
}
