import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {
	
	public static long calc(final long N, final long k){
		return k * (N - k) + N;
	}
	
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		final int N = sc.nextInt();
		
		System.out.println(calc(N, N / 2));
	}
	
}