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;
mt19937 rnd(time(0));
const long long inf = 0x3f3f3f3f3f3f3f3fLL;
const long long N = 3e5 + 10;
const long long MOD = 1e9 + 7;
long long m, n, c[30];
string s;
long long go(long long x) {
  long long pre = -1, cur = -1, res = 0;
  for (long long i = 0; i < n; i++) {
    if (s[i] < 'a' + x) pre = i, cur = i;
    if (s[i] == 'a' + x) cur = i;
    if (i - pre == m) {
      if (cur > pre)
        res++, pre = cur;
      else
        return -1;
    }
  }
  return res;
}
int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> m >> s;
  n = (long long)s.size();
  for (long long i = 0; i < n; i++) c[s[i] - 'a']++;
  for (long long i = 0; i < 26; i++) {
    long long x = go(i);
    if (x != -1) {
      for (long long j = 0; j < i; j++)
        for (long long k = 0; k < c[j]; k++) cout << (char)('a' + j);
      for (long long j = 0; j < x; j++) cout << (char)('a' + i);
      return 0;
    }
  }
  return 0;
}
