#include <bits/stdc++.h>
using namespace std;
int c[100], n, k;
int rec() {
  int ret = 0;
  for (int i = 0; i <= n - k; i++) {
    int res = 1;
    for (int j = 0; j < k; j++) {
      res *= c[i + j];
    }
    ret = max(ret, res);
  }
  return ret;
}
int main() {
  while (cin >> n >> k, n) {
    for (int i = 0; i < n; i++) {
      cin >> c[i];
    }
    int ck = rec();
    int ret = -1;
    for (int i = 0; i < n; i++) {
      for (int j = i + 1; j < n; j++) {
        swap(c[i], c[j]);
        ret = max(rec() - ck, ret);
      }
    }
    if (ret == -1)
      cout << "NOGAME" << endl;
    else
      cout << ret << endl;
  }
}
