#include "bits/stdc++.h"
#define in std::cin
#define out std::cout
#define rep(i,N) for(LL i=0;i<N;++i)
typedef long long int LL;

int main()
{
	LL N;
	in >> N;

	LL ans = 0;
	for (LL i = N; i >= 2; --i) ans += i * (i - 1) - 1;
	if (N > 1) ans += N + (N - 1);

	out << ans << std::endl;
}