#include <bits/stdc++.h>
using namespace std;
long long mod = 1000000007;
long long mod2 = 998244353;
long long mod3 = 1000003;
long long mod4 = 998244853;
long long mod5 = 1000000009;
long long inf = 1LL << 62;
int iinf = 1 << 30;
double pi = 3.141592653589793238462643383279L;
double eps = 1e-14;
int dh[4] = {1, -1, 0, 0};
int dw[4] = {0, 0, 1, -1};
int ddh[8] = {-1, -1, -1, 0, 0, 1, 1, 1};
int ddw[8] = {-1, 0, 1, -1, 1, -1, 0, 1};
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }
  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
long long gcd(long long a, long long b) {
  if (a < b) swap(a, b);
  if (b == 0) return a;
  if (a % b == 0) return b;
  return gcd(b, a % b);
}
long long lcm(long long a, long long b) {
  long long c = gcd(a, b);
  return a * b / c;
}
long long Pow(long long n, long long k) {
  if (k < 0) return 0;
  long long ret = 1;
  long long now = n;
  while (k > 0) {
    if (k & 1) ret *= now;
    now *= now;
    k /= 2;
  }
  return ret;
}
long long beki(long long n, long long k, long long md) {
  long long ret = 1;
  long long now = n;
  now %= md;
  while (k > 0) {
    if (k % 2 == 1) {
      ret *= now;
      ret %= md;
    }
    now *= now;
    now %= md;
    k /= 2;
  }
  return ret;
}
long long gyaku(long long n, long long md) { return beki(n, md - 2, md); }
long long popcount(long long n) {
  long long ret = 0;
  long long u = n;
  while (u > 0) {
    ret += u % 2;
    u /= 2;
  }
  return ret;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n, k;
  cin >> n >> k;
  string s;
  cin >> s;
  string t = s;
  reverse(t.begin(), t.end());
  s += t;
  int num = 26;
  int ma = 0;
  int now = 1;
  for (int i = 1; i < s.size(); i++) {
    int nu = s[i] - 'a';
    int nup = s[i - 1] - 'a';
    if (nu == nup)
      now++;
    else {
      if (nup < num) {
        num = nup;
        ma = now;
      } else if (nup == num) {
        ma = max(ma, now);
      }
      now = 1;
    }
  }
  int numm = s[2 * n - 1] - 'a';
  if (numm < num) {
    num = numm;
    ma = now;
  } else if (numm == num) {
    ma = max(ma, now);
  }
  if (k >= 14) {
    for (int i = 0; i < n; i++) {
      cout << (char)(num + 'a');
    }
    cout << endl;
    return 0;
  }
  vector<string> v;
  now = 1;
  for (int i = 1; i < s.size(); i++) {
    int nu = s[i] - 'a';
    int nup = s[i - 1] - 'a';
    if (nu == nup)
      now++;
    else {
      if (nup == num && now == ma && i >= n) {
        string y = s.substr(i - n, n);
        reverse(y.begin(), y.end());
        v.push_back(y);
      }
      now = 1;
    }
  }
  numm = s[2 * n - 1] - 'a';
  if (numm == num && now == ma) {
    string y = s.substr(2 * n - 1 - n, n);
    reverse(y.begin(), y.end());
    v.push_back(y);
  }
  sort(v.begin(), v.end());
  string ss = v[0], tt;
  for (int i = 0; i < k - 1; i++) {
    tt = ss;
    reverse(tt.begin(), tt.end());
    tt += ss;
    ss = tt.substr(ma, n);
    reverse(ss.begin(), ss.end());
    ma = min(ma * 2, n);
  }
  cout << ss << endl;
}
