// #pragma GCC target("avx")  // CPU 処理並列化
// #pragma GCC optimize("O3")  // CPU 処理並列化
// #pragma GCC optimize("unroll-loops")  // 条件処理の呼び出しを減らす
#include <bits/stdc++.h>
#include <complex>

// #include <iostream> // cout, endl, cin
// #include <string> // string, to_string, stoi
// #include <vector> // vector
// #include <algorithm> // min, max, swap, sort, reverse, lower_bound, upper_bound
// #include <utility> // pair, make_pair
// #include <tuple> // tuple, make_tuple
// #include <cstdint> // int64_t, int*_t
// #include <cstdio> // printf
// #include <map> // map
// #include <queue> // queue, priority_queue
// #include <set> // set
// #include <stack> // stack
// #include <deque> // deque
// #include <unordered_map> // unordered_map
// #include <unordered_set> // unordered_set
// #include <bitset> // bitset
// #include <climits>
// #include <cmath>
// #include <iomanip>
// #include <functional>
// #include <numeric>
// #include <random>
 
using namespace std;

#define int long long
#define pb push_back
#define eb emplace_back
// #define F first
// #define S second
#define FOR(i,a,b) for(int (i)=(a);(i)<(int)(b);(i)++)
#define rep(i,n) FOR(i,0,n)
#define RFOR(i,a,b) for(int (i)=(a);(i)>=(int)(b);(i)--)
#define rrep(i,n) RFOR(i,n,0)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define ve vector
#define vi vector<int>
#define vp vector<pair<int,int>>
#define vvi vector<vector<int>>
#define UNIQUE(a) sort(all(a)), a.erase(unique(all(a)), a.end())
#define Double double
// #define endl '\n'
 
template<typename T> using pq = priority_queue<T,vector<T>,greater<T>>; 
using ll = long long;
using UnWeightedGraph = vector<vector<int>>;
ll INF = LLONG_MAX / 4 - 100;
int IINF = INT_MAX / 4;
ll mod = 1e9 + 7;
int dx[] = {1,0,-1,0}, dy[] = {0,1,0,-1};
vector<ll> prime;
 
long double pi = 3.141592653589793238;
    
class fact {
public:
    long long fmod = 1e9+7;
    vector<long long> fac, finv, inv;
    fact (int n, long long Mod = 1e9+7) {
        fmod = Mod;
        fac = vector<long long>(n + 1, 0);
        finv = vector<long long>(n + 1, 0);
        inv = vector<long long>(n + 1, 0);
        fac[0] = fac[1] = 1;
        finv[0] = finv[1] = 1;
        inv[1] = 1; 
        for (int i = 2; i < n + 1; i++) {
            fac[i] = fac[i-1] * i % fmod;
            inv[i] = mod - inv[mod%i] * (mod/i) % mod;
            finv[i] = finv[i-1] * inv[i] % mod;
        }
    }
    ll nCr(ll n, ll r) {if(n < r) return 0; return fac[n] * finv[r] % fmod * finv[n-r] % fmod;}
    ll POW(ll a, ll b) {ll c = 1; while (b > 0) {if (b & 1) {c = a * c%fmod;}a = a * a%fmod; b >>= 1;}return c;}
    inline int operator [] (int i) {return fac[i];}
    ll DeBuG(ll n, ll r);
};
    
void DEBUG(vector<int> a) {for(int i=0;i<a.size();i++)cout<<a[i]<<" ";cout<<endl;}
void EMP(int x) {cout<<"!!!"<<x<<"!!!"<<endl;}
ll GCD(ll a, ll b) {ll c; while (b != 0) {c = a % b; a = b; b = c;}return a;}
ll LCM(ll a, ll b) {return (a / GCD(a, b)) * (b / GCD(a, b)) * GCD(a, b);}
ll POW(ll a, ll b) {ll c = 1; while (b > 0) {if (b & 1) {c = a * c%mod;}a = a * a%mod; b >>= 1;}return c;}
void PRI(ll n) {bool a[n + 1]; for (int i = 0; i < n + 1; i++) {a[i] = 1;}for (int i = 2; i < n + 1; i++) {if (a[i]) {prime.pb(i); ll b = i; while (b <= n) {a[b] = 0; b += i;}}}}
template <typename T> T chmin(T& a, T b) {if(a>b)a=b;return a;}
template <typename T> T chmax(T& a, T b) {if(a<b)a=b;return b;}
bool isSqrt(ll a) {return pow(sqrt(a),2) == a ? 1 : 0;}
void YesNo(bool a) {if (a) cout << "Yes"; else cout << "No"; cout << endl;}
void yesno(bool a) {if (a) cout << "yes"; else cout << "no"; cout << endl;}
void YESNO(bool a) {if (a) cout << "YES"; else cout << "NO"; cout << endl;}
double dis(int x1, int x2, int y1, int y2) {
    return sqrt((double)abs(x1-x2)*(double)abs(x1-x2)+(double)abs(y1-y2)*(double)abs(y1-y2));
}
int ceili(int x, int y) {
    if (x % y == 0) return x / y;
    else return x / y + 1;
}
unsigned int randxor() {
    static unsigned int x=123456789,y=362436069,z=521288629,w=88675123;
    unsigned int t;
    t=(x^(x<<11));x=y;y=z;z=w; return( w=(w^(w>>19))^(t^(t>>8)) );
}
 
uint64_t xor64(void) {
    static uint64_t x = 88172645463325252ULL;
    x = x ^ (x << 7);
    return x = x ^ (x >> 9);
}

class UnionFind {
private:
	vector<int> par;
public:
	UnionFind(int N) { par = vector<int>(N, -1); }
	int find(int x);
	ll size(int x);
	void unite(int x, int y);
	bool same(int x, int y);
};

int UnionFind::find(int x) {
	if (par[x] < 0) return x;
	else return par[x] = find(par[x]);
}
 
ll UnionFind::size(int x) {
	return -par[find(x)];
}
 
void UnionFind::unite(int x, int y) {
	x = find(x);
	y = find(y);
 	if (x == y) return;
	//大きい方に小さい方をくっ付ける
	if (size(x) < size(y)) swap(x, y);
	par[x] += par[y];
	par[y] = x;
}
 
bool UnionFind::same(int x, int y) {
	x = find(x);
	y = find(y);
	return x == y;
}

void solve() {
    int n; cin >> n;
    int k; cin >> k;
    string s; cin >> s;
    string t = s; reverse(all(t));
    s += t;
    char mi = 'z';
    rep (i, n) {
        chmin(mi, s[i]);
    }
    vector<int> streak(n*2);
    streak[0] = (s[0]==mi?1:0);
    int ma = streak[0];
    rep (i, 2*n-1) {
        if (s[i+1]==mi) streak[i+1] = streak[i]+1;
        else streak[i+1] = 0;
        chmax(ma, streak[i+1]);
    }
    chmin(ma, n);

    int len = ma;
    rep (i, k-1) {
        len *= 2;
        if (len >= n) {
            rep (j, n) cout << mi; cout << endl;
            return;
        }
    }

    len = n-len+ma;
    string an = string(len, 'z');
    FOR (i, n, 2*n) {
        if (streak[i] < ma) continue;
        if (streak[i] > ma) break;
        string tmp;
        rep (j, len) {
            tmp += s[i-j];
        }
        chmin(an, tmp);
    }


    rep (i, n-an.size()) cout << mi;
    cout << an << endl;
}
 
signed main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
}


Measured memory_bytes: 384