import java.util.*;
public class Soroban{
	public static void main(String args[])
	{
		Scanner s=new Scanner(System.in);
		long maxTama = s.nextLong();
		long maxTamaPosi = maxTama/2;
		System.out.println(maxTamaPosi+(maxTama-maxTamaPosi)*(maxTamaPosi+1));
	}
}