#include <bits/stdc++.h>
#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math")
using namespace std;
template <class t>
inline t read(t &x) {
  char c = getchar();
  bool f = 0;
  x = 0;
  while (!isdigit(c)) f |= c == '-', c = getchar();
  while (isdigit(c)) x = (x << 1) + (x << 3) + (c ^ 48), c = getchar();
  if (f) x = -x;
  return x;
}
template <class t, class... A>
inline void read(t &x, A &...a) {
  read(x);
  read(a...);
}
template <class t>
inline void write(t x) {
  if (x < 0)
    putchar('-'), write(-x);
  else {
    if (x > 9) write(x / 10);
    putchar('0' + x % 10);
  }
}
const int N = 5005;
char mc = 'z', s[N << 1];
int n, k, f[N << 1], ma, p;
bool compare(int l, int r) {
  for (; s[l] == s[r]; l++, r++)
    ;
  return s[l] < s[r];
}
signed main() {
  read(n, k);
  k = min(k, 15);
  scanf("%s", s + 1);
  for (int i = 1; i <= n; i++) s[n * 2 - i + 1] = s[i];
  for (int i = 1; i <= n; i++) s[i] < mc ? mc = s[i] : 1;
  for (int i = n; i; i--)
    f[i] = s[i] == mc ? f[i + 1] + 1 : 0, ma = f[i] > ma ? f[i] : ma;
  int rest = max(n - (ma << k - 1), 0);
  for (int i = 1; i <= n; i++)
    if (f[i] == ma && (!p || compare(i + ma, p))) p = i + ma;
  for (int i = 1; i <= n - rest; i++) putchar(mc);
  for (int i = 0; i < rest; i++) putchar(s[p + i]);
}
