import java.util.*;

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