By the end of 2005, the figure dropped to 3.8 million copies.

It was limited to 30,000 copies and used another cover, which is in black.

Later sales increased the figure to more than 800,000 copies.

Like the others, it was limited to to 300 copies.

At the university level sales grew more than 19 percent, to 176 million copies, between 1993 and 1998.

The sales of university books grew by almost 4 percent to 18.5 million copies from a year earlier.

By May 2009, sales had increased to over 4.1 million copies.

However, by 1999 it had dropped to 68 212 copies.

Sales of all his published books amount to more than 750,000 copies.

Each book is signed by the author and limited to no more than 200 copies.