#include <bits/stdc++.h>
using namespace std;
static const int N = 100;
int main() {
  int n, k, cnt, c[N], i, j, l, m, bcmax, acmax, x;
  while (1) {
    cin >> n >> k;
    if (n == 0 && k == 0) break;
    for (i = 0; i < n; i++) {
      cin >> c[i];
    }
    bcmax = 0;
    j = 0;
    for (i = 0; i <= n - k; i++) {
      cnt = k;
      x = 1;
      while (cnt) {
        x *= c[j];
        j++;
        cnt--;
      }
      bcmax = max(bcmax, x);
    }
    acmax = 0;
    for (i = 0; i < n; i++) {
      for (j = 0; j < n; j++) {
        if (i != j) {
          swap(c[i], c[j]);
          m = 0;
          for (l = 0; l <= n - k; l++) {
            cnt = k;
            x = 1;
            while (cnt) {
              x *= c[m];
              m++;
              cnt--;
            }
            acmax = max(acmax, x);
          }
          swap(c[i], c[j]);
        }
      }
    }
    if (acmax - bcmax >= 0)
      cout << acmax - bcmax << endl;
    else
      cout << "NO GAME" << endl;
  }
  return 0;
}
