#include<stdio.h>
int main()
{int a,b,c,d,e;
scanf("%i %i %i %i", &a, &b, &c, &d);
if(a<b){e=a;a=b;b=e;}
if(a<c){e=a;a=c;c=e;}
if(a<d){e=a;a=d;d=e;}
if(b<c){e=b;b=c;c=e;}
if(b<d){e=b;b=d;d=e;}
if(c<d){e=c;c=d;d=e;}
printf("%i",a*b+c*d);
return 0;
}