#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  string s;
  int k, n;
  cin >> n >> k >> s;
  vector<int> cnt(n, 0);
  char best = *min_element(s.begin(), s.end());
  if (k > 14) {
    for (int i = 0; i < n; ++i) cout << best;
  } else {
    if (k == 1) {
      string t = s, ans = s;
      reverse(t.begin(), t.end());
      s += t;
      for (int i = 0; i < n + 1; ++i) {
        if (ans > s.substr(i, n)) ans = s.substr(i, n);
      }
      cout << ans;
      return 0;
    }
    string t = s;
    reverse(t.begin(), t.end());
    string ans = s;
    s += t;
    k -= 1;
    int cnt = 0;
    for (int i = s.size() - 1; i >= 0; --i) {
      if (s[i] == best)
        cnt++;
      else {
        cnt = 0;
      }
      int get = min(n, cnt << k);
      if (i < n - get) {
        continue;
      }
      string tmp = s.substr(i - n + get, n - get);
      reverse(tmp.begin(), tmp.end());
      ans = min(ans, string(get, best) + tmp);
    }
    cout << ans;
  }
  return 0;
}
