Cannot Run Java Program That Is Using External Library From Command Line

I am reading the excellent book Algorithms. The author of this book is using his own libraries.

I have downloaded the libraries (it is a file called stdlib.jar) and I've store it in a directory called ~/Downloads(I am using a macbook pro).

Then I have created a project with IntelliJ Idea 14.1 using the default package (as it is the only way for a program to 'see' these libraries).

The program is running inside the ide, but because of the nature of this book, all the included code must be run from the command line.

The problem is that I cannot run for example the Average class from the command line because the system asks for the external library.

Specifically the error is :

I enter : java -cp . Average

and the Error I get is :

Exception in thread "main" java.lang.NoClassDefFoundError: StdIn
at Average.main(Average.java:11)
Caused by: java.lang.ClassNotFoundException: StdIn
at java.net.URLClassLoader$1.run(URLClassLoader.java:372)

[Code] ....

The Average class is the following :

public class Average {
public static void main(String[] args) {
//Average the numbers on StdIn
double sum = 0.0;
int cnt = 0;

[Code] .....