import java.util.*;
public class LightSwitchingPuzzle {
	
	
	 public static void main(String[] args) {
		 Scanner sc=new Scanner(System.in);
		 long n=sc.nextLong();
		 long N=n/2;
		 long ans=N*(N+1)/2;
		 N=(n-2)/2;
		 ans+=N*(N+1)/2;
		 
		 System.out.println(ans);
	 }


}