#include <algorithm>
#include <iostream>
#include <numeric>
#include <vector>
#include <string>
#include <bitset>
#include <queue>
#include <tuple>
#include <cmath>
#include <map>
#include <cstring>

template<typename T> bool chmax( T &a, const T &b ) { if ( a <= b ) { a = b; return ( true ); } else { return ( false ); } }
template<typename T> bool chmin( T &a, const T &b ) { if ( a >= b ) { a = b; return ( true ); } else { return ( false ); } }

using namespace std;

using ll = long long;
using ull = unsigned long long;

using Pint = pair<int, int>;
using Pll  = pair<ll, ll>;
using Pull = pair<ull, ull>;

#define eb emplace_back
#define pb push_back
#define mp make_pair
#define mt make_tuple

#define F first
#define S second

#define rep( i, n ) for ( int i = 0; i < (int)( n ); ++i )
#define reps( i, n ) for ( int i = 1; i <= (int)( n ); ++i )
#define rrep( i, n ) for ( int i = (int)( ( n ) - 1 ); i >= 0; --i )
#define rreps( i, n ) for ( int i = (int)( ( n ) ); i > 0; --i )
#define arep( i, v ) for ( auto &&i : ( v ) )

template<typename T> T gcd( const T a, const T b ) { return ( b ? gcd( b, a % b ) : a ); }
template<typename T> T lcm( const T a, const T b ) { return ( a / gcd( a, b ) * b ); }

#define ALL( c ) ( c ).begin(), ( c ).end()
#define RALL( c ) ( c ).rbegin(), ( c ).rend()
#define UNIQUE( c ) ( c ).erase( unique( ( c ).begin(), ( c ).end() ), ( c ).end() )

constexpr ll MOD = 1000000007LL;
template<typename T = ll> constexpr T MAX = numeric_limits<T>::max();

#define y0 y3487465
#define y1 y8687969
#define j0 j1347829
#define j1 j234892
#define next asdnext
#define prev asdprev

template<typename T = ll> class UnionFind {
public:
	UnionFind( T n ) { par.resize( n ); siz.resize( n ); rep( i, n ) { par[i] = i; siz[i] = 1; } }
	T find( T x ) { if ( x == par[x] ) return ( x ); else return( par[x] = find( par[x] ) ); }
	void unite( T x, T y ) { T xx = find( x ); T yy = find( y ); if ( xx == yy ) return;
		if ( siz[xx] <= siz[yy] ) swap( xx, yy ); par[yy] = xx; siz[xx] += siz[yy]; }
private:
	vector<T> par, siz;
};

template<typename T = ll> class CompareMax {
public:	T operator()( T a, T b ) { return ( max( a, b ) ); }
};
template<typename T = ll> class CompareMin {
public:	T operator()( T a, T b ) { return ( min( a, b ) ); }
};

template<typename T = ll, typename F = CompareMax<T>, T I = 0> class SegTree {
public:
	SegTree( T n ) { N = n; v.resize( 4 * n ); rep( i, 4 * n ) v[i] = I; }
	void update( T i, T x ) { i += N - 1; v[i] = x; while ( i > 0 ) {
			i = ( i - 1 ) / 2; v[i] = func( v[i * 2 + 1], v[i * 2 + 2] ); } }
	T query( T a, T b, T k, T l, T r ) {
		if ( r <= a || b <= l ) return ( I );
		if ( a <= l && r <= b ) return ( v[k] );
		else { T vl = query( a, b, k * 2 + 1, l, ( l + r ) / 2 );
			T vr = query( a, b, k * 2 + 2, ( l + r ) / 2, r );
			return ( func( vl, vr ) ); }
	}
private:
	T N; F func; vector<T> v;
};

template<typename T = ll> T solveLIS( const vector<T> &v ) {
	vector<T> dp( v.size(), numeric_limits<T>::max() );
	rep( i, v.size() ) {
		*lower_bound( ALL( dp ), v[i] ) = v[i];
	}
	return ( distance( dp.begin(), lower_bound( ALL( dp ), numeric_limits<T>::max() ) ) );
}

template<typename T = ll> T power( T a, T b, T m = MOD ) {
	T res = 1;
	while ( b > 0 ) { if ( b & 1 ) res = res * a % m;
		a = a * a % m; b >>= 1; }
	return ( res );
}

/*
constexpr ll COMBSIZE = 500010;
ll fact[COMBSIZE];
ll inv[COMBSIZE];
ll inv_fact[COMBSIZE];

template<typename T> void initComb( T n, T m = MOD )
{
	fact[0] = fact[1] = inv_fact[0] = inv_fact[1] = 1;
	inv[1] = 1;
	for ( int i = 2; i < n; i++ ) {
		fact[i] = ( fact[i - 1] * i ) % m;
		inv[i] = m - inv[m % i] * ( m / i ) % m;
		inv_fact[i] = inv_fact[i - 1] * inv[i] % m;
	}
}

template<typename T> T comb( T n, T r, T m = MOD )
{
	if ( n < r ) return ( 0 );
	if ( n < 0 || r < 0 ) return ( 0 );
	return ( fact[n] * ( inv_fact[r] * inv_fact[n - r] % m ) % m );
}
*/

void replace( string &s, string t, string r ) {
	string::size_type p = 0;
	while ( ( p = s.find( t, p ) ) != string::npos ) {
		s.replace( p, t.length(), r );
		p += r.length();
	}
}


int main()
{
	ll N, K; cin >> N >> K;
	string s; cin >> s;
	string t = s;

	sort( ALL( t ) );

	ll cnt = 0, cnttmp = 0;
	vector<int> v( 26 );
	rep( i, N )
	{
		if ( s[i] == t[0] )
		{
			++cnttmp;
		}
		else
		{
			chmax( cnt, cnttmp );
			cnttmp = 0;
		}
	}
	chmax( cnt, cnttmp );

	string ans = "";
	if ( ( K >= 13 ) || ( K >= N ) )
	{
		rep( i, N ) ans += t[0];
	}
	else
	{
		rep( k, K - 1 )
		{
			string tmp = s;
			rrep( i, N ) tmp += s[i];

			vector<pair<string, string>> vtmp;
			rrep( i, N * 2 )
			{
				if ( ( tmp[i] == t[0] ) && ( i >= N - 1 ) )
				{
					bool ok = true;
					rep( j, cnt - 1 )
					{
						if ( tmp[i] != tmp[i - 1 - j] )
						{
							ok = false; break;
						}
					}

					if ( ok )
					{
						string p1 = tmp.substr( i + 1 - N, N );
						string p2 = ""; rrep( i, N ) p2 += p1[i];
						vtmp.eb( mp( p1, p2 ) );
					}
				}
			}
			sort( ALL( vtmp ), []( pair<string, string> a, pair<string, string> b ) {
					return ( a.S < b.S );
				} );
			s = vtmp[0].F;
			cnt *= 2;
			vtmp.clear();
		}

		if ( K == 1 )
		{
			if ( s.back() == t[0] )
			{
				ll tmpcnt = 0;
				rrep( i, N )
				{
					if ( s[i] == t[0] )
					{
						++tmpcnt;
					}
					else
					{
						break;
					}
				}
				if ( tmpcnt == cnt ) cnt *= 2;
			}
		}
		string tmp = s;
		rrep( i, N ) tmp += s[i];
		vector<string> vtmp;
		rep( i, N )
		{
			if ( tmp[i] == t[0] )
			{
				bool ok = true;
				rep( j, cnt - 1 )
				{
					if ( tmp[i] != tmp[i + 1 + j] )
					{
						ok = false; break;
					}
				}

				if ( ok )
				{
					vtmp.eb( tmp.substr( i, N ) );
				}
			}
		}

		if ( vtmp.size() == 0 )
		{
			ans = s;
		}
		else
		{
			sort( ALL( vtmp ) );
			ans = vtmp[0];
		}
	}

	cout << ans << endl;

	return ( 0 );
}


Measured memory_bytes: 12928