#include <stdio.h>

int main(void)
{
	long long n,a1=0,a2=0;
	while(scanf("%lld",&n)==1)
	{
		if(n>a1)
		{
			a2=a1;
			a1=n;
		}
		else if(n>a2)
		{
			a2=n;
		}
	}
	printf("%lld",a1*a2);
}