package yukicoder111;
import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);
		long len=sc.nextLong();
		len=(len-1)/2;
		
		//n=2k+1
			//1+3+5+7+9+11+   +n-2(2k-1)
			//=1/2*k*2k=k^2
			//abababababababa 15
			//ababababababa
			//babababababab
			//abababababa
			//bababababab
			//ababababa
			//babababab
			//abababa
			//bababab
			//ababa
			//babab
			//aba
			//bab
		
		System.out.println(len*len);
	}
}