#include <stdio.h>
inline void swap(unsigned int *a, unsigned int *b)
{
	unsigned int c=*a;
	*a=*b;
	*b=c;
}
int main()
{
	unsigned int v[5];
	unsigned int i=0;
	for(i=0;i<4;++i)
	{
		scanf("%d", &v[i]);
	}
	unsigned int j=0;
	unsigned int aux=0;
	for(i=0;i<4;++i)
	{
		for(j=0;j<4;++j)
		{
			if(v[j]<v[i])
				swap(&v[i],&v[j]);
		}
	}

	printf("%d\n", v[0]*v[1]+v[2]*v[3]);
	return 0;
}