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 <class T>
int getbit(T s, int i) {
  return (s >> i) & 1;
}
template <class T>
T onbit(T s, int i) {
  return s | (T(1) << i);
}
template <class T>
T offbit(T s, int i) {
  return s & (~(T(1) << i));
}
template <class T>
int cntbit(T s) {
  return __builtin_popcount(s);
}
template <class T>
inline T gcd(T a, T b) {
  T r;
  while (b != 0) {
    r = a % b;
    a = b;
    b = r;
  }
  return a;
}
string s;
long long m;
vector<long long> kt[27];
set<long long> st;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> m >> s;
  long long n = s.size();
  for (long long i = 0, _b = n; i < _b; i++) {
    kt[s[i] - 'a'].push_back(i);
  }
  for (long long c = 0, _b = 26; c < _b; c++) {
    bool ok = true;
    long long dem = 0;
    for (long long i = n - 1, _b = m - 1; i >= _b; i--) {
      auto z = st.lower_bound(i - m + 1);
      if (z != st.end() && *z <= i) {
        i = *z;
        continue;
      }
      auto g = lower_bound(kt[c].begin(), kt[c].end(), i - m + 1);
      if (g != kt[c].end() && *g <= i) {
        i = *g;
        dem++;
      } else {
        ok = false;
        break;
      }
    }
    if (ok) {
      for (long long i = 0, _b = c; i < _b; i++)
        for (long long j = 0, _b = kt[i].size(); j < _b; j++)
          cout << char(i + 'a');
      for (long long i = 0, _b = dem; i < _b; i++) cout << char(c + 'a');
      return 0;
    }
    for (auto x : kt[c]) st.insert(x);
  }
  return 0;
}
