ZJUT_1174

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