#include<cstdio>
#include<Cstring>
#define N 10001
int i,j,k,l,n;char c[N],x[N],y[N];
int main()
{
	scanf("%d%d%s",&n,&k,c+1),k--;
	for(i=1,j=n<<1;i<=n;c[j--]=c[i++])y[i-1]='z';
	for(i=j=1;i<=n;i=j)
	{
		while(j<=n&&c[i]==c[j])j++;
		if(k>12||j-i<<k>=n)memset(x,c[i],n);
		else memset(x,c[i],j-i<<k),memcpy(x+(j-i<<k),c+j,n-(j-i<<k));
		if(strcmp(x,y)<0)memcpy(y,x,n);
	}
	return 0*printf("%s\n",y);
}