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