// 1+3+5+...

import java.util.Scanner;
public class SumOdd
{
	public static int S (int n)
	{
		if (n==1)
			return 1;
		else
			return n + S(n-2);
	}
	public static void main(String[] args)
	{
		Scanner input = new Scanner(System.in);

		int n = input.nextInt();
		if(n%2 != 0)
		{
			int f = S(n);
			System.out.println("the result is:"+f);
		}
		else
			System.out.println("Error - not odd!");
	}
}