We invite you to solve the English version of the RTSdécouverte monthly problem:

**House of Cards**

To construct a house of cards, take two cards and put them together in a triangle. You have built a one-storey house.

To build a second floor, add a pair of cards next to the first pair. Then, place a card horizontally and place a third pair of cards on top of it.

Continuing like this, you can (in theory) build a house of cards with as many storeys as you wish.

How many cards do you need to build 100-storey house?