#include <bits/stdc++.h>
using namespace std;
const int M = 1000000007;
void Solution() {
  long long n, m;
  cin >> n >> m;
  if (n == 1)
    cout << 0 << "\n";
  else if (n == 2)
    cout << m << "\n";
  else
    cout << 2 * m << "\n";
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int tc;
  cin >> tc;
  while (tc--) Solution();
  return 0;
}
