import java.util.*;
import java.math.*;
import java.io.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int L = sc.nextInt();
		long ans = 0;
		for(int i = 2; i < L; i += 2) {
			ans += (L - i);
		}
		System.out.println(ans);
	}
}