#include <bits/stdc++.h>
using namespace std;
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long t = 1, n, k, fact, a, b;
  cin >> t;
  while (t--) {
    cin >> a >> b;
    if (a == 1)
      cout << "0\n";
    else if (a == 2)
      cout << b << "\n";
    else
      cout << 2 * b << "\n";
  }
  return 0;
}
