Once upon a time, there was a child named Maliang. His father and mother had died long ago, and he earned his living by collecting firewood and cutting grass. He likes to learn painting since he was young, but he doesn't even have a pen!

However, he is still determined to learn painting and practice diligently every day. When he went to the mountain to gather firewood, he broke a branch and learned to draw birds in the sand. When he went to the river to cut grass, he dipped the grass roots in the river water and learned to draw fish on the shore stones. In the evening, he came home, took a piece of charcoal, and on the wall of the cave, he painted again and again the things that had painted during the day. Without a pen, he still learns to draw. If I tell you how many paintings Maliang painted on the sand, on the shore stones and on the cave walls, can you calculate the total number of paintings Maliang painted?

In the past year by year, Maliang 's study of painting has never been interrupted. Around his cave, there are layers of paintings, densely packed with paintings. Of course, progress was also rapid, and the birds he drew could almost sing, while the fish he drew could almost swim. Once, he drew a little hen at the entrance of the village, and there were eagles circling around in the sky above the entrance. Once, he drew a black haired wolf behind the mountain, which scared the cows and sheep not to eat grass behind the mountain.

But Maliang doesn't have a pen yet! He thought, how great it would be to have a pen for himself!