import java.io.InputStream;
import java.io.PrintStream;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Domino solver = new Domino(new Scanner(System.in));
        solver.solve();
        sc.close();
    }

    public static class Domino {
        private Scanner scanner;
        private PrintStream print;
        InputStream stream;

        public Domino(Scanner scanner) {
            this.scanner = scanner;
            print = new PrintStream(System.out);
        }

        public void setPrintStream(PrintStream o) {
            if(print!=null) {
                print.close();
            }       
            print = o;
        }

        public void solve() {
            int n = scanner.nextInt();
            int result = 0;
            for(int i=0; i<=n; ++i) {
                if(i == 0) {
                    result += sumAll(1, n);             
                } else {
                    result += sumAll(2*i, i+n);
                } 
            }
            print.println(result);
        }

        private int sumAll(int n1, int n2) {
            return (n2*(n2+1) - n1*(n1-1)) / 2;
        }
    }
}