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;
void fre() {
  freopen("c://test//input.in", "r", stdin);
  freopen("c://test//output.out", "w", stdout);
}
template <class T1, class T2>
inline void gmax(T1 &a, T2 b) {
  if (b > a) a = b;
}
template <class T1, class T2>
inline void gmin(T1 &a, T2 b) {
  if (b < a) a = b;
}
const int N = 1e5 + 10, M = 0, Z = 1e9 + 7, inf = 0x3f3f3f3f;
template <class T1, class T2>
inline void gadd(T1 &a, T2 b) {
  a = (a + b) % Z;
}
int n, m;
char a[N];
char b[N];
void solve() {
  for (char c = 'a'; c <= 'z'; ++c) {
    bool flag = 1;
    int p = 0;
    for (int i = 1; i <= n; ++i) {
      if (a[i] <= c) p = i;
      if (i >= p + m) {
        flag = 0;
        break;
      }
    }
    if (flag) {
      int p = 0;
      int g = 0;
      int lastc = -1;
      for (int i = 1; i <= n; ++i) {
        if (a[i] < c)
          b[++g] = a[i], p = i;
        else if (a[i] == c)
          lastc = i;
        if (i >= p + m) {
          b[++g] = c;
          p = lastc;
        }
      }
      b[g + 1] = 0;
      sort(b + 1, b + g + 1);
      puts(b + 1);
      return;
    }
  }
}
int main() {
  while (~scanf("%d%s", &m, a + 1)) {
    n = strlen(a + 1);
    solve();
  }
  return 0;
}
