#include<iostream>
using namespace std;
int main(){
	int n,sum=0,sum1;
	cin>>n;
	for(int i=1;i<=n;i++){
		sum1=1;
		for(int j=1;j<=i;j++){
			sum1=sum1*j;
		}
		sum=sum+sum1;
	}
	cout<<sum<<endl;
	return 0;
}