#include <iostream>
using namespace std;

int n,k;
int in[101];

int calc() {
    int ans = 0;
    for(int i=0; i+k<=n; ++i) {
        int tmp = 1;
        for(int j=0; j<k; ++j)
            tmp *= in[i+j];
        ans = max(ans,tmp);
    }
    return ans;
}

int main() {
    while(cin>>n>>k, n|k) {
        for(int i=0; i<n; ++i) cin>>in[i];
        int ck = calc(),ans = 0;
        for(int i=0; i<n; ++i) 
            for(int j=0; j<i; ++j) {
                swap(in[i],in[j]);
                int t = calc();
                if(t >= ck) ans = max(ans, t);
                swap(in[i],in[j]);
            }
        if(ans == 0) cout<<"NO GAME"<<endl;
        else cout<<ans-ck<<endl;
    }
}