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