import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner koko = new Scanner(System.in);
        long n = koko.nextInt();
        if(n%2==0){
            long a = n*n/4+n;
            System.out.println(a);
        }else{
            long a = (n+1)/2;
            long ans = n*a-a*a+n;
            System.out.println(ans);
        }
    }
    
}