#include <bits/stdc++.h>
using namespace std;
int n, k;
char s[10000 + 5], Mn, Mx, ans[10000 + 5], tmp[10000 + 5];
long long read() {
  long long x = 0, F = 1;
  char c = getchar();
  while (c < '0' || c > '9') {
    if (c == '-') F = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    x = x * 10 + c - '0';
    c = getchar();
  }
  return x * F;
}
void cal(char *s, int t) {
  int np = n, len = 0;
  while (np >= 1 && s[np] == Mn) np--, len++;
  while (k > 0 && len < n) len *= 2, k--;
  if (len >= n) {
    for (int i = 1; i <= n; i++) ans[i] = Mn;
    return;
  }
  for (int i = 1; i <= len; i++) tmp[i] = Mn;
  for (int i = len + 1; i <= n; i++) tmp[i] = s[np--];
  for (int i = 1; i <= n; i++)
    if (tmp[i] < ans[i]) {
      for (int j = 1; j <= n; j++) ans[j] = tmp[j];
      return;
    } else if (tmp[i] > ans[i])
      return;
}
int main() {
  n = read(), k = read();
  scanf("%s", s + 1);
  Mn = 'z', Mx = 'a';
  for (int i = 1; i <= n; i++) {
    Mn = min(Mn, s[i]), Mx = max(Mx, s[i]);
    s[n * 2 - i + 1] = s[i];
    ans[i] = 'z';
  }
  if (s[n] == Mn) cal(s, k);
  for (int i = n; i <= 2 * n; i++)
    if (s[i] == Mn) cal(s + i - n, k - 1);
  printf("%s", ans + 1);
}
