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