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