#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    long long n, m;
    cin >> n >> m;
    if (n == 1)
      cout << "0\n";
    else if (n == 2)
      cout << m << "\n";
    else
      cout << 2 * m << "\n";
  }
  return 0;
}
