import java.util.Scanner;

public class No71 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long N = sc.nextLong();
		long x;
		if(N % 2 == 0) {
			x = N/2;
		}else {
			x =(N-1)/2;
		}
		
		System.out.println((x+1) * (N-x+1) -1);
	}
}