#include <bits/stdc++.h>
const int LG = 21;
const int FN = 400005;
const long long MOD = 1e9 + 7;
const long long INF = 1e9;
const long long INFLL = 1e18;
using namespace std;
int cx[4] = {-1, 0, 1, 0};
int cy[4] = {0, -1, 0, 1};
long long inq(long long x, long long y) {
  if (!y) return 1 % MOD;
  long long l = inq(x, y / 2);
  if (y % 2) return l * l % MOD * x % MOD;
  return l * l % MOD;
}
long long rev(long long x) { return inq(x, MOD - 2); }
bool __precomputed_combinatorics = 0;
vector<long long> __fact, __ufact, __rev;
void __precompute_combinatorics() {
  __precomputed_combinatorics = 1;
  __fact.resize(FN);
  __ufact.resize(FN);
  __rev.resize(FN);
  __rev[1] = 1;
  for (int i = 2; i < FN; i++)
    __rev[i] = MOD - __rev[MOD % i] * (MOD / i) % MOD;
  __fact[0] = 1, __ufact[0] = 1;
  for (int i = 1; i < FN; i++)
    __fact[i] = __fact[i - 1] * i % MOD,
    __ufact[i] = __ufact[i - 1] * __rev[i] % MOD;
}
long long fact(int x) {
  if (!__precomputed_combinatorics) __precompute_combinatorics();
  return __fact[x];
}
long long cnk(int n, int k) {
  if (!__precomputed_combinatorics) __precompute_combinatorics();
  return __fact[n] * __ufact[n - k] % MOD * __ufact[k] % MOD;
}
const int N = 100500;
int n;
vector<pair<int, long long> > graph[N];
int sz[N];
void dfs(int v, int p) {
  sz[v] = 1;
  for (auto u : graph[v])
    if (u.first != p) {
      dfs(u.first, v);
      sz[v] += sz[u.first];
    }
}
long long dist[N];
void dfs2(int v, int p) {
  for (auto u : graph[v])
    if (u.first != p) {
      dist[u.first] = dist[v] + u.second;
      dfs2(u.first, v);
    }
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long n, k;
  cin >> n >> k;
  string s;
  cin >> s;
  if (k >= 14) {
    sort((s).begin(), (s).end());
    for (int(i) = 0; (i) != (n); (i)++) cout << s[0];
    return 0;
  }
  return 1;
}
