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>
struct str {
  char x0;
  int y0;
} ans[100010];
str Str(char a, int b) {
  str A;
  A.x0 = a;
  A.y0 = b;
  return A;
}
bool operator<(str a, str b) {
  if (a.x0 == b.x0) return a.y0 > b.y0;
  return a.x0 < b.x0;
}
std::set<str> S;
char x[100010];
int check[100010];
int main() {
  int a, b;
  scanf("%d%s", &b, x + 1);
  a = strlen(x + 1);
  for (int i = 1; i <= 26; i++) {
    int k = 1;
    for (int j = 1; j <= a; j++) {
      if (x[j] == i + 'a' - 1) {
        k = k > j - b + 1 ? k : j - b + 1;
        for (; k <= j; k++)
          if (check[k] == 0) check[k] = i;
      }
    }
    for (int j = 1; j <= a - b + 1; j++) {
      if (check[j] == 0) {
        for (k = 1; k <= a; k++)
          if (x[k] == i + 'a' - 1) printf("%c", i + 'a' - 1);
        goto u;
      }
    }
    for (int j = 1; j <= a - b + 1; j++) {
      if (check[j] == i) {
        for (int k = j + b - 1;; k--) {
          if (x[k] == i + 'a' - 1) {
            printf("%c", i + 'a' - 1);
            j = k;
            break;
          }
        }
      }
    }
    return 0;
  u:;
  }
}
