Competitive Programming

#include <bits/stdc++.h>
using namespace std;
int main()
{
   int x1,x2,y1,y2;
   cin>>x1>>y1>>x2>>y2;
   while(x2>=x1&&y2>=y1)
   {
       cout<<(x2-x1)*(y2-y1)<<"\n";
       cin>>x1>>y1>>x2>>y2;
   }
}