#include <iostream>
#include<fstream>
using namespace std;
ifstream f("input");
ofstream g("output");
int i,v[5],aux,j,s;
int main()
{for(i=1;i<=4;i++)
    f>>v[i];
for(i=1;i<4;i++)
    for(j=1;j<=4;j++)
        if(v[i]>v[j])
            {aux=v[i];
            v[i]=v[j];
            v[j]=aux;}
s=v[1]*v[2]+v[3]*v[4];
g<<s;
return 0;
}