#include <iostream>
using namespace std;

int v[5];
int aux;
int suma;

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