#include<bits/stdc++.h>
using namespace std;
int n,ans;
int main(){
	  cin>>n;
	  for(int i=1;i<=n;i++){
	  	int g=1;
	  	for(int j=1;j<=i;j++){
	  		g*=j;
		  }

	ans+=g;
	    } 
		cout<<ans;                  
	return 0;
}
/**************************************************************
	Problem: 1019
	User: chenjingqi
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/