#include <iostream>

using namespace std;

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