A - Most Unstable Array.cpp

#define ll long long
#include<bits/stdc++.h>

using namespace std;

int main()
{
    ll T;
    cin>>T;
    while(T--)
    {
        ll n, m;
        cin>>n>>m;
        if(n==1)
            cout<<"0"<<endl;
        else if(n==2)
            cout<<m<<endl;
        else
            cout<<2*m<<endl;
    }
    return 0;
}