代码：

#include<bits/stdc++.h>
using namespace std;
unsigned long long niu(int a){	
unsigned long long sum=1,s=0;	
  for (int i=1;i<=a;i++){		
    sum*=i;		
    s+=sum;	
  }	
  return s;	
}
int n;
int main()
{	
  cin>>n;	
  cout<<niu(n);	
return 0;
}