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;
int inf_int = 2e9;
long long inf_ll = 2e18;
const double pi = 3.1415926535898;
long long binpow(long long a, long long n) {
  if (n == 0) {
    return 1;
  }
  long long res = 1;
  while (n) {
    if (n % 2 == 1) {
      res *= a;
    }
    a *= a;
    n /= 2;
  }
  return res;
}
int gcd(int a, int b) {
  while (b) {
    a %= b;
    swap(a, b);
  }
  return a;
}
const double EPS = 1e-7;
int siz(long long x) {
  if (x < 1e1) {
    return 1;
  } else if (x < 1e2) {
    return 2;
  } else if (x < 1e3) {
    return 3;
  } else if (x < 1e4) {
    return 4;
  } else if (x < 1e5) {
    return 5;
  } else if (x < 1e6) {
    return 6;
  } else if (x < 1e7) {
    return 7;
  } else if (x < 1e8) {
    return 8;
  } else if (x < 1e9) {
    return 9;
  } else if (x < 1e10) {
    return 10;
  }
}
int m;
string s;
map<char, vector<int> > mmap;
vector<int> indices;
vector<bool> triggered;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> m >> s;
  string ans;
  for (int i = 0; i < s.size(); i++) {
    mmap[s[i]].push_back(i);
  }
  triggered.assign(s.size(), 0);
  int mx = -1;
  for (int i = 0; i < s.size() - m + 1;) {
    int mn = 125;
    for (int j = i; j < i + m; j++) {
      mn = min(mn, (int)s[j]);
    }
    mx = max(mn, mx);
    for (int j = i + m - 1; j >= i; j--) {
      if ((int)s[j] == mn) {
        i = j + 1;
        break;
      }
    }
  }
  for (int i = (int)'a'; i < mx; i++) {
    for (int j = 0; j < mmap[(char)i].size(); j++) {
      triggered[mmap[(char)i][j]] = 1;
      ans.push_back((char)i);
    }
  }
  for (int i = 0; i < s.size() - m + 1;) {
    bool c = 0;
    for (int j = i; j < i + m; j++) {
      if (triggered[j] == 1) {
        c = 1;
        i = j + 1;
      }
    }
    if (!c) {
      for (int j = i + m - 1; j >= i; j--) {
        if ((int)s[j] == mx) {
          triggered[j] = 1;
          ans += mx;
          i = j + 1;
        }
      }
    }
  }
  cout << ans << endl;
  return 0;
}
