#include <bits/stdc++.h>
using namespace std;
const int N = 5005;
char s[N];
int p[N];
signed main() {
  int n, K;
  long long res = 1;
  cin >> n >> K;
  for (int i = 2; i <= K; ++i) {
    res *= 2;
    if (res >= n) {
      res = n;
      break;
    }
  }
  cin >> (s + 1);
  for (int i = n + 1; i <= n + n; ++i) s[i] = s[i - n];
  reverse(s + n + 1, s + n + n + 1);
  char ch = *min_element(s + 1, s + n + 1);
  int cnt = (s[1] == ch);
  for (int i = 2; i <= n + n; ++i)
    if (s[i] == ch && s[i] == s[i - 1])
      ++cnt;
    else
      p[i - 1] = cnt, cnt = (s[i] == ch);
  p[n + n] = cnt;
  int mx = *max_element(p + n + 1, p + n + n + 1);
  res *= mx;
  if (res >= n) {
    for (int i = 1; i <= n; ++i) cout << ch;
    return 0;
  }
  string S = "", tmp;
  for (int i = n + 1; i <= n + n; ++i)
    if (p[i] == mx) {
      tmp = "";
      for (int j = 1; j <= res; ++j) tmp += ch;
      for (int j = i - p[i]; j > i - p[i] - (n - res); --j) tmp += s[j];
      if (S == "")
        S = tmp;
      else
        S = min(S, tmp);
    }
  cout << S;
  return 0;
}
