#include <iostream>

using namespace std;

int main()
{
    int v[4],ok=0,i,aux;
    cin>>v[0]>>v[1]>>v[2]>>v[3];
    while (ok==0)
    {
        ok=1;
        for (i=0;i<3;i++)
            if(v[i]<v[i+1])
            {
                aux=v[i];
                v[i]=v[i+1];
                v[i+1]=aux;
                ok=0;
            }
    }
    cout<<v[0]*v[1]+v[2]*v[3];
    return 0;
}