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