import java.util.Scanner;

class Test {
	public static void main(String[] args) throws Exception {
		Scanner in = new Scanner(System.in);
		int l = in.nextInt();

		long ans = 0;
		for(int i=2; i<l; i+=2) {
			ans += (l - i);
		}

		System.out.println(ans);
	}
}