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;
char buf[100002];
string s;
bool flag[100002];
int im[100002];
int bit[100002];
void add(int i, int x) {
  i++;
  while (i < 100002) {
    bit[i] += x;
    i += i & -i;
  }
}
int sum(int i) {
  int r = 0;
  i++;
  while (i > 0) {
    r += bit[i];
    i -= i & -i;
  }
  return r;
}
string F;
int main() {
  cin >> m;
  scanf("%s", buf);
  s = buf;
  int n = s.size();
  char en;
  for (int i = 0; i < 26; i++) {
    char target = 'a' + i;
    for (int k = 0; k < n; k++) {
      if (s[k] <= target) {
        im[k] = 1;
      } else {
        im[k] = 0;
      }
      if (k) {
        im[k] += im[k - 1];
      }
    }
    bool ng = false;
    for (int k = 0; k < n; k++) {
      if (k + m - 1 < n) {
        int P = im[k + m - 1];
        if (k) {
          P -= im[k - 1];
        }
        if (P == 0) {
          ng = true;
          break;
        }
      }
    }
    if (ng == false) {
      en = target;
      break;
    }
  }
  char target = en;
  int L = -1;
  for (int k = 0; k < n; k++) {
    if (s[k] == target) {
      L = k;
    }
    if (s[k] < target) {
      add(k, 1);
      flag[k] = true;
    }
    if (k >= m - 1) {
      int c = sum(k) - sum(k - m);
      if (c == 0) {
        flag[L] = true;
        add(L, 1);
      }
    }
  }
  for (int i = 0; i < n; i++) {
    if (flag[i]) {
      F.push_back(s[i]);
    }
  }
  sort(F.begin(), F.end());
  printf("%s\n", F.c_str());
  return 0;
}
