#include <bits/stdc++.h> 
using namespace std;
int main()
{
	int a,b=1,c=0;
	cin>>a;//3
	for (int j=a;j>=1;j--)
	{
		for (int i=1;i<=j;i++)
		{
			b=b*i;
		}
		c=c+b;
		b=0;
	}
	cout<<c;
}