#include <stdio.h>
#include <stdlib.h>

int main()
{
    int a,b,c,d,aux,rez;
    scanf("%d",&a);
    scanf("%d",&b);
    scanf("%d",&c);
    scanf("%d",&d);
    if(a<c)
    {
        aux = a;
        a = c;
        c = aux;
    }
    if(a<d)
    {
        aux = a;
        a = d;
        d = aux;
    }
    if(b<d)
    {
        aux = b;
        b = d;
        d = aux;
    }
    if(b<c)
    {
        aux = b;
        b = c;
        c = aux;
    }
    rez = a*b+c*d;
    printf("%d",rez);
    return 0;
}