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;
double Fib(double x, double z);
string BinDec(long long x);
string StringInt(long long x);
unsigned long long StringInt(string x);
long long BinDec(string x);
unsigned long long POWMOD(unsigned long long x, unsigned long long y,
                          unsigned long long mod);
unsigned long long POWE(long long, long long);
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int x, i, j, q[30] = {}, qq[30] = {}, c[104000] = {}, s = 0;
  string a, ans;
  cin >> x >> a;
  for (i = 0; i < a.size(); i++) q[a[i] - 'a']++;
  for (i = 0; i <= a.size() - x; i++) {
    int d = 0, maxi = 1e6, k = 0;
    for (j = i; j < i + x; j++) {
      if (c[j] == 1) {
        d = 1;
        break;
      }
      if (a[j] <= maxi) {
        k = j;
        maxi = a[j];
      }
    }
    if (d == 0) {
      ans += a[k];
      c[k] = 1;
    }
  }
  bool r = 0;
  for (i = 0; i < ans.size(); i++) qq[ans[i] - 'a']++;
  for (i = 28; i >= 0; i--) {
    if (qq[i] != 0 && r == 0) {
      r = 1;
      continue;
    }
    if (r == 0) continue;
    for (j = 0; j < q[i] - qq[i]; j++) ans += (i + 'a');
  }
  sort(ans.begin(), ans.end());
  cout << ans;
  return 0;
}
double Fib(double x, double z) {
  int i = 0;
  double f = x, r = x, t;
  for (i = 2; i < z; i++) {
    t = f;
    f += r;
    r = t;
  }
  return f;
}
string BinDec(long long x) {
  string z;
  while (1) {
    if (x % 2 == 0)
      z += '0';
    else
      z += '1';
    x /= 2;
    if (x == 0) break;
  }
  reverse(z.begin(), z.end());
  return z;
}
long long BinDec(string x) {
  long long i;
  unsigned long long z = 1, a = 0;
  for (i = x.size() - 1; i >= 0; i--) {
    if (x[i] == '1') a += z;
    z *= 2;
  }
  return a;
}
unsigned long long StringInt(string x) {
  unsigned long long z = 0, i;
  for (i = 0; i < x.size(); i++) {
    z *= 10;
    z += (x[i] - '0');
  }
  return z;
}
string StringInt(long long x) {
  string z;
  while (x != 0) {
    z += (x % 10 + '0');
    x /= 10;
  }
  reverse(z.begin(), z.end());
  return z;
}
unsigned long long POWMOD(unsigned long long base, unsigned long long exp,
                          unsigned long long mod) {
  unsigned long long res = 1;
  while (exp > 0) {
    if (exp % 2 == 1) res = (res * base);
    res %= mod;
    exp /= 2;
    base = (base * base);
    base %= mod;
  }
  return res % mod;
}
unsigned long long POWE(long long base, long long exp) {
  unsigned long long res = 1;
  while (exp > 0) {
    if (exp % 2 == 1) res = (res * base);
    exp /= 2;
    base = (base * base);
  }
  return res;
}
