The Spirit of Logic smiled and vanished back into the textbook. Petya didn't finish his homework in five minutes, but when he finally closed his book two hours later, he felt like a giant. He didn't need to download an answer key—he had become one.

"Wait, Petya!" the Spirit squeaked. "If you download that file, you aren't just getting answers—you’re losing your 'brain-muscles'!"

"The reshebnik is a shortcut to a dead end," the Spirit whispered. "Arginskaya didn't write these problems to torture you; she wrote them to make you a thinker."

Petya looked at the "Download" button, then at the complex problem in his book. He realized that the "click" of a mouse was easy, but the "aha!" moment of solving a puzzle was better. He closed the browser tab, took a deep breath, and began to draw a diagram for the area problem.