# Simple Combinatorics

# Card houses

Slavik wants to become an artist of original genre, so he constantly engaged in manipulation with a variety of objects. At the moment, all his spare time he is busy in building houses of cards. He has even managed to build a **4** - storey house, where he used **26** cards. At the technology lesson secretly from the teacher he demonstrated his ability before classmates to build a house with **3** floors, with just **15** cards. "Arts" of the future artist are given in the pictures from his mobile phone below.

Currently Slavik is interested in the question of mathematical content: how many cards you need to have to build a house with **n** floors? He asks you to help him, as with mathematics Slavik has problems ...

#### Input

Positive integer **n** - the number of the floors in a house to be built. This number is no more than `10`

.^{8}

#### Output

Print the number of cards needed for the construction of a house with **n** floors.

3

15

4

26