import java.util.Scanner;

public class No71 {

	public static void main(String[] args) {
		
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		scanner.close();
		
		int ans = n / 2;
		
		System.out.println( (long)(n-ans+1)*(ans+1) - 1);

	}

}