A_Most_Unstable_Array.cpp

#include <bits/stdc++.h>
using namespace std;

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    int t;
    cin >> t;
    while (t--)
    {
        long long n, m;
        cin >> n >> m;
        if (n == 1)
            cout << 0LL << "\n";
        else if (n == 2)
            cout << m << "\n";
        else
            cout << 2LL * m << "\n";
    }

    return 0;
}