import java.util.*;

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