import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		scan.close();
		int x;
		if(N % 2 == 0) {
			x = N / 2;
		}else {
			x = N / 2 + 1;
		}
		long ans = (long)(x + 1) * (N - x + 1) - 1;
		System.out.println(ans);
	}
}