#include<stdio.h>

int main(void){
	int n,k,c,cc,tmp,c_max;
	int card[102];
	int i,j,l,m;

	while(scanf("%d %d",&n,&k) && n != 0 && k != 0){
		for(i=0;i<n;i++)
			scanf("%d",&card[i]);
		c_max=0;
		cc = 0;
		tmp = 1;
		for(i=0;i<=n-k;i++){
			for(j=i;j<k+i;j++){
				tmp*=card[j];
			}
			if(tmp > cc)
				cc = tmp;
			tmp=1;
		}

		for(i=0;i<n-1;i++){
			for(j=i+1;j<n;j++){
				tmp = card[i];
				card[i] = card[j];
				card[j] = tmp;

				c = 1;
				for(l=0;l<=n-k;l++){
					for(m=l;m<k+l;m++){
						c*=card[m];
					}
					if(c > c_max)
						c_max = c;
					c=1;
				}

				tmp = card[i];
				card[i] = card[j];
				card[j] = tmp;
			}
		}
	
		if(c_max - cc >= 0)
			printf("%d\n",c_max-cc);
		else
			printf("NO GAME\n");
	}
	return 0;
}