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 maxn = 1010;
const int mod = 1e9 + 7;
char s[100010];
char ans[100010];
int vis[30];
set<int> st;
inline void RI(int &x) {
  char c;
  while ((c = getchar()) < '0' || c > '9')
    ;
  x = c - '0';
  while ((c = getchar()) >= '0' && c <= '9') x = (x << 3) + (x << 1) + c - '0';
}
int main() {
  int m;
  RI(m);
  cin >> s;
  int n = strlen(s);
  st.clear();
  int ma = 0;
  for (int i = 0; i <= n - m;) {
    memset(vis, -1, sizeof(vis));
    for (int j = i; j <= i + m - 1; j++) {
      vis[s[j] - 'a'] = j;
    }
    int j;
    for (j = 0; j <= 25; j++) {
      if (vis[j] != -1) {
        ma = max(ma, s[vis[j]] - 'a');
        st.insert(vis[j]);
        break;
      }
    }
    i = vis[j] + 1;
  }
  for (int i = 0; i <= n - 1; i++) {
    if (s[i] - 'a' < ma) st.insert(i);
  }
  int sum = 0;
  for (set<int>::iterator it = st.begin(); it != st.end(); it++) {
    sum++;
    ans[sum] = s[*it];
  }
  sort(ans + 1, ans + sum + 1);
  cout << ans + 1 << endl;
  return 0;
}
