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 int oo = 0x3f3f3f3f;
string in;
class compare {
 public:
  bool operator()(int a, int b) {
    if (in[a] == in[b]) return a > b;
    return in[a] < in[b];
  }
};
int main() {
  ios_base::sync_with_stdio(false);
  set<int, compare> s;
  int count[26], ans[26];
  int m, i, j;
  int maxi;
  cin >> m >> in;
  memset(count, 0, sizeof count);
  memset(ans, 0, sizeof ans);
  for (i = 0; i < in.size(); i++) {
    count[in[i] - 'a']++;
  }
  for (j = 0; j < min(m, (int)in.size()); j++) {
    s.insert(j);
  }
  i = 0;
  maxi = 0;
  if (j >= in.size()) {
    for (i = 0; i < 26; i++) {
      if (count[i]) printf("%c\n", i + 'a');
      return 0;
    }
  }
  while (j < in.size()) {
    int at = *s.begin();
    maxi = max(in[at] - 'a', maxi);
    s.erase(at);
    while (i <= at) {
      s.erase(i);
      i++;
      if (j < in.size()) {
        s.insert(j);
        j++;
      }
    }
    ans[in[at] - 'a']++;
  }
  int print = 0;
  for (i = 0; i < maxi; i++) {
    while (count[i]--) {
      printf("%c", i + 'a');
    }
  }
  while (ans[i]--) {
    printf("%c", i + 'a');
  }
  printf("\n");
  return 0;
}
