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 <typename T, typename T1>
ostream &operator<<(ostream &out, pair<T, T1> obj) {
  out << "(" << obj.first << "," << obj.second << ")";
  return out;
}
template <typename T, typename T1>
ostream &operator<<(ostream &out, map<T, T1> cont) {
  typename map<T, T1>::const_iterator itr = cont.begin();
  typename map<T, T1>::const_iterator ends = cont.end();
  for (; itr != ends; ++itr) out << *itr << " ";
  out << endl;
  return out;
}
template <typename T>
ostream &operator<<(ostream &out, set<T> cont) {
  typename set<T>::const_iterator itr = cont.begin();
  typename set<T>::const_iterator ends = cont.end();
  for (; itr != ends; ++itr) out << *itr << " ";
  out << endl;
  return out;
}
template <typename T>
ostream &operator<<(ostream &out, multiset<T> cont) {
  typename multiset<T>::const_iterator itr = cont.begin();
  typename multiset<T>::const_iterator ends = cont.end();
  for (; itr != ends; ++itr) out << *itr << " ";
  out << endl;
  return out;
}
template <typename T,
          template <typename ELEM, typename ALLOC = allocator<ELEM>> class CONT>
ostream &operator<<(ostream &out, CONT<T> cont) {
  typename CONT<T>::const_iterator itr = cont.begin();
  typename CONT<T>::const_iterator ends = cont.end();
  for (; itr != ends; ++itr) out << *itr << " ";
  out << endl;
  return out;
}
template <typename T, unsigned int N, typename CTy, typename CTr>
typename enable_if<!is_same<T, char>::value, basic_ostream<CTy, CTr> &>::type
operator<<(basic_ostream<CTy, CTr> &out, const T (&arr)[N]) {
  for (auto i = 0; i < N; ++i) out << arr[i] << " ";
  out << endl;
  return out;
}
template <typename T>
T gcd(T a, T b) {
  T min_v = min(a, b);
  T max_v = max(a, b);
  while (min_v) {
    T temp = max_v % min_v;
    max_v = min_v;
    min_v = temp;
  }
  return max_v;
}
template <typename T>
T lcm(T a, T b) {
  return (a * b) / gcd(a, b);
}
template <typename T>
T fast_exp_pow(T base, T exp, T mod) {
  long long res = 1;
  while (exp) {
    if (exp & 1) {
      res *= base;
      res %= mod;
    }
    exp >>= 1;
    base *= base;
    base %= mod;
  }
  return res % mod;
}
struct compare {
 public:
  bool operator()(const pair<char, int> &obj1, const pair<char, int> &obj2) {
    if (obj1.first == obj2.first) return obj1.second < obj2.second;
    return obj1.first > obj2.first;
  }
};
int M, N, last = -1;
bool used[100010];
string word, result;
map<pair<char, int>, bool> can_use, out_of_stack;
priority_queue<pair<char, int>, vector<pair<char, int>>, compare> que;
int main() {
  scanf("%d", &M);
  cin >> word;
  N = word.size();
  memset(used, false, sizeof(used));
  for (auto i = 0; i < M; ++i) {
    que.push(make_pair(word[i], i));
    can_use[make_pair(word[i], i)] = true;
    out_of_stack[make_pair(word[i], i)] = false;
  }
  for (auto i = M; i <= N; ++i) {
    while (!que.empty() && out_of_stack[que.top()]) que.pop();
    auto ret = que.top();
    if (i - M > last && can_use[ret]) {
      result += ret.first;
      can_use[ret] = false;
      used[ret.second] = true;
      last = ret.second;
    }
    if (i < N) {
      que.push(make_pair(word[i], i));
      can_use[make_pair(word[i], i)] = true;
      out_of_stack[make_pair(word[i], i)] = false;
    }
    can_use[make_pair(word[i - M], i - M)] = false;
    out_of_stack[make_pair(word[i - M], i - M)] = true;
  }
  sort(result.begin(), result.end());
  char biggest = result.back();
  for (auto i = 0; i < N; ++i) {
    if (!used[i] && word[i] < biggest) result += word[i];
  }
  sort(result.begin(), result.end());
  cout << result << endl;
  return 0;
}
