#include <bits/stdc++.h>
using namespace std;
void print() {
  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";
}
int main() {
  int t;
  cin >> t;
  while (t--) print();
}
