package main

import (
	"fmt"
)

func main() {
	var N int
	fmt.Scanf("%d\n", &N)
	if N <= 2 {
		fmt.Println(N)
	} else {
		var r int = N
		for i := 0; i < N - 2; i ++ {
			r += (N - 1 - i) * (N - 2 - i)
		}
		fmt.Println(r)
	}

}
