#include<iostream>
#include<cstdio>
using namespace std;
int main(){
	int n;
	cin>>n;
	unsigned long long f[51]={1},tot[51]={0};
	for(int i=1;i<=50;i++){
		f[i]=f[i-1]*i;
		tot[i]=tot[i-1]+f[i];
	}
	cout<<tot[n];
	return 0; 
}