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;
inline void read(int &x) {
  register int c = getchar();
  x = 0;
  int neg = 0;
  for (; ((c < 48 || c > 57) && c != '-'); c = getchar())
    ;
  if (c == '-') {
    neg = 1;
    c = getchar();
  }
  for (; c > 47 && c < 58; c = getchar()) {
    x = (x << 1) + (x << 3) + c - 48;
  }
  if (neg) x = -x;
}
inline void write(int x) {
  char buffor[12];
  register int i = 0;
  int neg = 0;
  if (x < 0) {
    neg = 1;
    x = -x;
  }
  do {
    buffor[i++] = (x % 10) + '0';
    x /= 10;
  } while (x);
  i--;
  if (neg) putchar('-');
  while (i >= 0) putchar(buffor[i--]);
}
inline void writeln(int x) {
  write(x);
  putchar('\n');
}
inline void read(long long &x) {
  register int c = getchar();
  x = 0;
  int neg = 0;
  for (; ((c < 48 || c > 57) && c != '-'); c = getchar())
    ;
  if (c == '-') {
    neg = 1;
    c = getchar();
  }
  for (; c > 47 && c < 58; c = getchar()) {
    x = (x << 1) + (x << 3) + c - 48;
  }
  if (neg) x = -x;
}
inline void write(long long x) {
  char buffor[21];
  register int i = 0;
  int neg = 0;
  if (x < 0) {
    neg = 1;
    x = -x;
  }
  do {
    buffor[i++] = (x % 10) + '0';
    x /= 10;
  } while (x);
  i--;
  if (neg) putchar('-');
  while (i >= 0) putchar(buffor[i--]);
}
inline void writeln(long long x) {
  write(x);
  putchar('\n');
}
const int N = 2e5 + 5;
int n, m;
string s;
void enter() {
  cin >> m >> s;
  n = ((int)(s).size());
  s = ' ' + s + ' ';
}
bool check(char x) {
  int Last = 0;
  for (int i = (1), _b = (n); i <= _b; ++i) {
    if (i - Last > m) return false;
    if (s[i] <= x) {
      Last = i;
    }
  }
  return true;
}
void process() {
  char c;
  for (c = 'a'; c <= 'z'; ++c)
    if (check(c)) break;
  vector<char> ans;
  int Last = 0, last_c = 0;
  for (int i = (1), _b = (n); i <= _b; ++i) {
    if (i - Last > m) {
      Last = last_c;
      ans.push_back(c);
    }
    if (s[i] < c) {
      Last = i;
      ans.push_back(s[i]);
    } else {
      if (s[i] == c) last_c = i;
    }
  }
  if (((int)(ans).size()) == 0) ans.push_back('a');
  sort(ans.begin(), ans.end());
  for (int i = (0), _b = (((int)(ans).size())); i < _b; ++i) cout << ans[i];
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  enter();
  process();
  return 0;
}
