#include<iostream>
using namespace std;

int main()
{
int a,b,c,d,aux;
cin>>a>>b;
if(a<b)
{
aux=a;
a=b;
b=aux;
}
cin>>c;
if(c>a)
{
aux=a;
a=c;
c=aux;
}
else if(c>b)
{
aux=b;
b=c;
c=aux;
}
cin>>d;
if(d>a)
{
aux=a;
a=d;
d=aux;
}
else if(d>b)
{
aux=d;
d=b;
b=aux;
}
cout<<(a*b)+(c*d);
return 0;
}