#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
const int INF = (1<<30);
const ll INFLL = (1ll<<60);
const ll MOD = (ll)(1e9+7);

#define l_ength size

void mul_mod(ll& a, ll b){
	a *= b;
	a %= MOD;
}

void add_mod(ll& a, ll b){
	a = (a<MOD)?a:(a-MOD);
	b = (b<MOD)?b:(b-MOD);
	a += b;
	a = (a<MOD)?a:(a-MOD);
}

vector<string> v;

int main(void){
	int n,i,k,p=1,q,m=0;
	string s,t,ans;
	cin >> n >> k; --k;
	cin >> s;
	t = s;
	reverse(s.begin(),s.end());
	t += s;
	reverse(s.begin(),s.end());
	for(i=0; i<n; ++i){
		v.push_back(t.substr(i,n));
	}
	sort(v.begin(),v.end());
	while(p<n && v[0][p-1] == v[0][p]){
		++p;
	}
	q = p;
	while(k){
		q *= 2;
		if(q > n){
			break;
		}
		--k;
	}
	q -= p;
	for(i=0; i<q; ++i){
		if(m<n){
			ans.push_back(v[0][0]);
			++m;
		}
	}
	for(i=0; i<n; ++i){
		if(m<n){
			ans.push_back(v[0][i]);
			++m;
		}
	}
	cout << ans << endl;
	return 0;
}
