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