#include<stdio.h>
int main()
{
	unsigned long long n,S=0,i,pro=1;
	scanf("%llu",&n);
	while(n>50||n<1)
	{
		scanf("%llu",&n);
	}
	for(i=1;i<=n;i++)
	{
		pro=pro*i;
		S=S+pro;
	}
	printf("%llu",S);
	return 0;
}