import java.util.*;

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