#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int t;
  cin >> t;
  while (t--) {
    long long int n, m, sum = 0;
    cin >> n >> m;
    long long int a[5] = {0};
    if (n == 1)
      cout << "0" << endl;
    else if (n == 2)
      cout << m << endl;
    else
      cout << (2 * m) << endl;
  }
}
