#include <bits/stdc++.h>
using namespace std;
int main(void) {
  int n, k;
  cin >> n >> k;
  string s;
  cin >> s;
  string t = s;
  reverse(t.begin(), t.end());
  s += t;
  vector<string> kouho;
  for (int i = 0; i < n; i++) {
    kouho.push_back(s.substr(i, n));
  }
  sort(kouho.begin(), kouho.end());
  char a = kouho[0][0];
  string ans = "";
  int i = 0;
  while (ans.size() < n && kouho[0][i] == a) {
    for (int j = 0; j < pow(2, min(20, k - 1)) && ans.size() < n; j++) {
      ans.push_back(a);
    }
    i++;
  }
  while (ans.size() < n) {
    ans.push_back(kouho[0][i]);
    i++;
  }
  cout << ans << endl;
  return 0;
}
