import java.util.Scanner;
public class Yuki71{
	public static void main(String[] arg){
		Scanner sc = new Scanner(System.in);
		int n;
		long res;
		n = sc.nextInt();
		if(n % 2 == 0){
			res = (long)(n/2)*(long)(n/2+1)+(long)(n/2);
		}else{
			res = (long)(n/2+1)*(long)(n/2+1)+(long)(n/2);
		}
		System.out.println(res);
	}
}