package yukicoder111;
import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);
		int len=sc.nextInt();
		long ans=0;
		int nlen=len;
		while(nlen>=3){
			ans+=len-nlen+1;
			nlen-=2;


			//abababababababa 15
			//ababababababa
			//babababababab
			//abababababa
			//bababababab
			//ababababa
			//babababab
			//abababa
			//bababab
			//ababa
			//babab
			//aba
			//bab
		}
		System.out.println(ans);
	}
}