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>
const double pi = acos(1.0 * (-1));
using namespace std;
const int INF = 2147483647;
const long long mod = 1000000007;
int main() {
  int n;
  string str;
  cin >> n;
  cin >> str;
  int pos = -1;
  for (int i = 0; i < 26; i++) {
    int now = 0;
    bool flag = true;
    for (int j = 0; j < str.length(); j++) {
      if (str[j] - 'a' <= i)
        now = 0;
      else
        now++;
      if (now >= n) {
        flag = false;
        break;
      }
    }
    if (flag) {
      pos = i;
      break;
    }
  }
  int now = 0;
  int last = -1;
  int sum = 0;
  for (int i = 0; i < str.length(); i++) {
    if (str[i] - 'a' == pos) last = i;
    if (str[i] - 'a' >= pos) {
      now++;
      if (now >= n) {
        sum++;
        i = last;
        now = 0;
      }
    } else
      now = 0;
  }
  vector<int> res;
  for (int i = 0; i < str.length(); i++)
    if (str[i] - 'a' < pos) res.push_back(str[i] - 'a');
  for (int i = 0; i < sum; i++) res.push_back(pos);
  sort(res.begin(), res.end());
  for (int i = 0; i < res.size(); i++) cout << (char)('a' + res[i]);
  return 0;
}
