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;
int arr[27];
int a = 0;
int A_A = (int)'a';
queue<string> ss;
queue<int> indexs;
void get(char let) {
  string s = ss.front();
  ss.pop();
  int index = indexs.front();
  indexs.pop();
  int last = -1;
  int b = s.length();
  int temp = min(a, b);
  for (int x = index; x < temp; x++) {
    if (s[x] == let) {
      last = x;
    }
    if (s[x] < let) {
      arr[(int)s[x] - A_A]++;
      indexs.push(0);
      ss.push(s.substr(x + 1));
      return;
    }
  }
  if (last != -1 && a == temp)
    arr[(int)let - A_A]++;
  else
    return;
  if (last != b) {
    ss.push(s.substr(last + 1));
    indexs.push(temp - last - 1);
  }
}
int main() {
  string s;
  cin >> a;
  cin >> s;
  int l = s.length();
  bool check = true;
  char let;
  for (int x = 0; x < 26; x++) {
    check = true;
    int last = -1;
    for (int y = 0; y < s.length(); y++) {
      if ((int)s[y] - A_A <= x) {
        last = y;
      }
      if (y - last >= a) {
        check = false;
        break;
      }
    }
    if (check) {
      let = (char)(A_A + x);
      break;
    }
  }
  ss.push(s);
  indexs.push(0);
  while (!ss.empty()) {
    get(let);
  }
  for (int x = 0; x < 26; x++) {
    while (arr[x] > 0) {
      cout << (char)(A_A + x);
      arr[x]--;
    }
  }
  cout << endl;
}
