#include<bits/stdc++.h>
using namespace std;
int X1,Y1,X2,Y2;
int X3,Y3,X4,Y4;
int main(){
cin>>X1>>Y1>>X2>>Y2;
cin>>X3>>Y3>>X4>>Y4;
if(X3>=X2||Y3>=Y2){
cout<<0;
return 0;
}
// 面积=长乘宽
printf("%.2lf",(X3-X2)*1.0*(Y3-Y2));
return 0;
}
/**************************************************************
Problem: 1841
User: admin
Language: C++
Result: Wrong Answer
****************************************************************/