import java.util.*;

public class Main {
	
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		long n=sc.nextLong();
		long ans=0;
		for(int i=0;i<n;i++){
			long ansk=0;
			long ue=i;
			long shita=n-i;
			ansk=ue*(shita+1)+shita;
			ans=Math.max(ans,ansk)	;	
		}
		System.out.println(ans);
	}}