#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
int main(int argc, char const argv[])
{
ios::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
int t;
cin>>t;
while(t–)
{
ll m,n;
ll x,y;
cin>>m>>n>>x>>y;
ll a=n/2;
ll ans=0;
ll f=2x;
ans+=(amin(y,f));
ans=m;
if(n%2==1)
{
ans+=((m/2)*(min(f,y)));
if(m%2==1)
{
ans+=min(x,y);
}
}
cout<<ans<<"\n";
}
return 0;
}