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>
inline void gn(T &x) {
  x = 0;
  T f = 1;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  x *= f;
}
template <typename T>
inline void gt(T x) {
  if (!x) return;
  gt(x / 10);
  putchar(x % 10 + '0');
}
const long long MAXN = 1e6 + 10;
long long t, n, m, ans;
long long MOD = 1e9 + 7, inf = 0x1f1f1f1f;
double eps = 1e-5;
char a[MAXN];
vector<long long> f[33];
long long pa[MAXN], cnt[MAXN], xx, yy, r, s;
long long find(long long x) { return x == pa[x] ? x : pa[x] = find(pa[x]); }
int main() {
  long long i, j, k, l, ca = 0;
  cin >> m >> a + 1;
  l = strlen(a + 1);
  for (i = 1; i <= l; i++) {
    f[a[i] - 'a'].push_back(i);
    pa[i] = i;
  }
  for (i = 25; i >= 0; i--) {
    l = f[i].size();
    long long flag = 0;
    for (j = l - 1; j >= 0; j--) {
      long long x = f[i][j];
      cnt[x] = 1;
      r = s = 0;
      if (cnt[r = find(x - 1)]) {
        pa[r] = x;
        cnt[x] += cnt[r];
      }
      if (cnt[s = find(x + 1)]) {
        pa[s] = x;
        cnt[x] += cnt[s];
      }
      if (cnt[x] >= m) {
        flag = 1;
        pa[r] = r;
        pa[s] = s;
        cnt[x] = 0;
      } else
        f[i][j] = 0;
    }
    if (flag) {
      xx = i;
      break;
    }
  }
  for (i = 0; i <= xx; i++) {
    l = f[i].size();
    for (j = 0; j < l; j++) {
      if (f[i][j]) a[++n] = 'a' + i;
    }
  }
  a[n + 1] = '\0';
  cout << a + 1 << endl;
  return 0;
}
