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 MX = 3e5 + 9;
const long double eps = -0.00000001;
const long long mod = 1e9 + 7;
int a[MX];
bool cmp(int a, int b) { return (a > b); }
vector<char> ans;
bool ok[MX];
int main() {
  int k;
  cin >> k;
  string s;
  cin >> s;
  int l = s.length();
  for (int i = 0; i <= l - k; i++) {
    int id = i;
    for (int j = i; j < i + k; j++) {
      if (s[j] <= s[id]) {
        id = j;
      }
    }
    ans.push_back(s[id]);
    i = id;
    ok[id] = 1;
  }
  sort(ans.begin(), ans.end());
  char mx = ans.back();
  for (int j = 0; j < l; j++) {
    if (s[j] < mx && !ok[j]) {
      ans.push_back(s[j]);
    }
  }
  sort(ans.begin(), ans.end());
  for (int i = 0; i < ans.size(); i++) {
    cout << ans[i];
  }
  return 0;
}
