#include <bits/stdc++.h>
using namespace std;
int main() {
  while (1) {
    int data[101], i, j, k, result;
    int N, K;
    cin >> N >> K;
    if (N == 0 && K == 0) break;
    for (i = 0; i < N; i++) cin >> data[i];
    int maxv = -1;
    for (i = 0; i <= N - K; i++) {
      result = 1;
      for (j = i; j < i + K; j++) result *= data[j];
      maxv = max(result, maxv);
    }
    int maxv2 = -1;
    int result2;
    for (i = 0; i < N; i++) {
      for (j = 0; j < N; j++) {
        if (i != j) {
          swap(data[i], data[j]);
          for (k = 0; k <= N - K; k++) {
            result2 = 1;
            for (int l = k; l < k + K; l++) result2 *= data[l];
            maxv2 = max(result, maxv2);
          }
          swap(data[i], data[j]);
        }
      }
    }
    int ans = maxv2 - maxv;
    if (ans >= 0)
      cout << ans << endl;
    else
      cout << "NO GAME" << endl;
  }
  return 0;
}
