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

class Main {
	
	public static void out (Object o) {
		System.out.println(o);
	}
	
	public static void main (String[] args) throws IOException {
		BufferedReader br = 
			new BufferedReader(new InputStreamReader(System.in));
		
		long n = Long.parseLong(br.readLine());
		n = (n - 1) / 2;
		out(n * n);
	}
}