#include<stdio.h>

int main(){
	int S=0,n,i,j,factorial;
	scanf("%d",&n);
	if(n==0)
		printf("0");
	else{
		for(i=1;i<=n;i++){
			factorial=1;
			for(j=1;j<=i;j++)
				factorial*=j;
			S+=factorial;
		}
	}
	printf("%d",S);
	return 0;
}