import java.util.*;
 

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		long ans=0;
		for(int i=1;i<n;i++){
			long sita=n-i;
			ans=Math.max(ans,(sita+1)*i+sita);
		}
		System.out.println(ans);
	}
}