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 MAX_L = 1e5 + 100, AZ = 26;
char St[MAX_L];
int A[MAX_L];
bool used[MAX_L];
int cnt[AZ];
int L, M;
vector<pair<int, int> > events;
void check(int c) {
  events.clear();
  for (int i = 0; i < int(L); ++i) used[i] = (A[i] < c);
  int cntm = 0, last = -1, lastgood = -1;
  for (int i = 0; i < L;) {
    while (i < L && !used[i] && i - last <= M - 1) {
      if (A[i] == c) lastgood = i;
      ++i;
    }
    if (i == L) break;
    if (used[i]) {
      last = i;
      ++i;
      continue;
    }
    if (A[i] == c) lastgood = i;
    if (lastgood > last)
      ++cntm, last = lastgood, ++i;
    else
      return;
  }
  for (int i = 0; i < int(c); ++i)
    for (int k = 0; k < int(cnt[i]); ++k) putchar(i + 'a');
  for (int k = 0; k < int(cntm); ++k) putchar(c + 'a');
  putchar('\n');
  exit(0);
}
int main() {
  scanf("%d\n", &M);
  gets(St);
  L = strlen(St);
  for (int i = 0; i < int(L); ++i) A[i] = St[i] - 'a', ++cnt[A[i]];
  for (int z = 0; z < int(AZ); ++z) check(z);
  assert(0);
  return 0;
}
