#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k;
  while (1) {
    cin >> n >> k;
    if (n == 0 && k == 0) break;
    int a[101] = {};
    for (int i = 0; i < n; i++) cin >> a[i];
    int ck = -1;
    for (int i = 0; i <= n - k; i++) {
      int t = 1;
      for (int j = 0; j < k; j++) t *= a[j + i];
      if (ck < t) ck = t;
    }
    int ck2 = -1;
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < n; j++) {
        if (i == j) continue;
        swap(a[i], a[j]);
        for (int l = 0; l <= n - k; l++) {
          int t = 1;
          for (int m = 0; m < k; m++) t *= a[m + l];
          if (ck2 < t) ck2 = t;
        }
        swap(a[i], a[j]);
      }
    }
    if (ck2 - ck)
      cout << "NO GAME" << endl;
    else
      cout << ck2 - ck << endl;
  }
  return 0;
}
