#include<stdio.h>
int main()
{
	int n, S=0, x,z,k;
	scanf("%d", &n);
	for (z=1;z<=n;z++)
	{
		int y = 1;
		for (x = 1; x <= z; x++)
			k=(y *= x);
		S += k;
	}
	printf("%d", S);
}