#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll inf = 1e18;
const int N = 2 * 1e5 + 10;
ll res;
ll a[N];
void solve() {
  ll n, k;
  cin >> n >> k;
  if (n == 1) {
    cout << 0 << "\n";
    return;
  }
  if (n == 2) {
    cout << k << "\n";
    return;
  }
  cout << 2 * k << "\n";
}
int main(int argc, char const *argv[]) {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  ll t = 1;
  cin >> t;
  while (t--) {
    solve();
  }
}
