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