#include <iostream>

using namespace std;

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