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;
struct comp {
  bool operator()(const pair<char, int>& a, const pair<char, int>& b) {
    if (a.first != b.first) return a.first < b.first;
    return a.second > b.second;
  }
};
int counts[26];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  string s;
  map<char, int> sres;
  int m;
  cin >> m;
  cin >> s;
  for (auto i : s) counts[i - 'a']++;
  int n = s.size();
  s.append(100500, (char)(255));
  if (m > n) {
    char c = 255;
    for (auto i : s) c = min(c, i);
    cout << c;
  } else {
    pair<char, int> cRes = {'z' + 1, m};
    for (int i = m - 1; i >= 0; i--) {
      if (cRes.first > s[i]) {
        cRes = {s[i], i};
      }
    }
    sres[cRes.first]++;
    set<pair<char, int>, comp> setOfLetters;
    int currI = cRes.second + m;
    int DELTA = m;
    for (int i = currI - m; i < currI; i++) setOfLetters.insert({s[i], i});
    for (int i = currI; i < n; i++) {
      setOfLetters.insert({s[i], i});
      setOfLetters.erase({s[i - DELTA], i - DELTA});
      if (i == currI) {
        sres[setOfLetters.begin()->first]++;
        currI = setOfLetters.begin()->second + m;
      }
    }
    auto lastIt = sres.end();
    lastIt--;
    char lastChar = lastIt->first;
    for (char i = 'a'; i < lastChar; i++) {
      cout << string(counts[i - 'a'], i);
    }
    cout << string(lastIt->second, lastIt->first);
  }
  return 0;
}
