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;
template <typename T, typename U>
inline void smin(T &a, U b) {
  if (a > b) a = b;
}
template <typename T, typename U>
inline void smax(T &a, U b) {
  if (a < b) a = b;
}
char str[111111];
vector<int> pos[26];
set<int> s;
set<int>::iterator it;
int main() {
  int M, id;
  scanf("%d %s", &M, str);
  int N = strlen(str);
  for (int i = 0; i < N; i++) pos[str[i] - 'a'].push_back(i);
  s.insert(-1);
  s.insert(N);
  for (int i = 0; i < 26; i++) {
    for (int j = 0, sz = pos[i].size(); j < sz; j++) {
      s.insert(pos[i][j]);
    }
    int fl = 0;
    for (it = s.begin(); it != s.end();) {
      int first = *it;
      it++;
      if ((*it) > first + M) break;
      if ((*it) == N) {
        fl = 1;
        break;
      }
    }
    if (fl) {
      id = i;
      break;
    }
  }
  for (int i = 0; i < id; i++) {
    for (int j = 0, sz = pos[i].size(); j < sz; j++) printf("%c", 'a' + i);
  }
  int ct = 0;
  for (int i = 0, sz = pos[id].size(); i < sz; i++) s.erase(pos[id][i]);
  for (int i = 0, sz = pos[id].size(); i < sz; i++) {
    it = s.lower_bound(pos[id][i]);
    int first = *it;
    it--;
    if (first - (*it) <= M) continue;
    if (i < sz - 1 && pos[id][i + 1] - (*it) <= M) continue;
    ct++;
    s.insert(pos[id][i]);
  }
  while (ct--) printf("%c", 'a' + id);
  puts("");
  return 0;
}
