#include<bits/stdc++.h>
#include<string.h>
#include<math.h>
#include<ctype.h>

#define ull unsigned long long
#define ll long long
#define pb push_back
#define mp make_pair
#define SS stringstream
#define allof(x) (x).begin(),(x).end()
#define gsize(x) (x).size()
#define modb7 (ll)1000000007


using namespace std;

int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int testcases;
cin>>testcases;
while(testcases--)
{
long int n,m,x,y,a,b;
cin>>n>>m>>x>>y;
if(x>=y)
{
    a=y;
    b=0;
}
else
{
    a=x;
    if(x*2<=y)
    {
        b=x;
    }
    else
    {
        b=y-x;
    }
}
long int noe=n*m;
long ans=(noe+1)/2*max(a,b)+(noe)/2*min(a,b);
cout<<ans<<endl;
}
return 0;
}