#include <bits/stdc++.h>
using namespace std;
int main() {
  std::ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  int t;
  cin >> t;
  while (t--) {
    int n, m;
    cin >> n >> m;
    cout << min(2, n - 1) * m << "\n";
  }
  return 0;
}
