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