import java.util.*;
import java.io.*;
import java.awt.geom.*;
import static java.util.Arrays.*;

class Main{
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);
		int D = Integer.parseInt(stdIn.next());
		int max = 0;
		for(int i=1;i<=D/2;i++){
			int s = i*(D/2-i);
			if(max<s){
				max = s;
			}
		}
		out.println(max);
		out.flush(); 
	}
}