#include<cstdio>
#include<algorithm>
using namespace std;
int i,a[10];
int main()
{
	//freopen("test.in","r",stdin);
	//freopen("test.out","w",stdout);
	for(i=1;i<=4;i++) scanf("%d",&a[i]);
	sort(a+1,a+4+1);
	printf("%d\n",a[4]*a[3]+a[2]*a[1]);
	return 0;
}