favorite We need a little bit of your help to keep things running, click on this banner to learn more

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 ...



Positive integer n - the number of the floors in a house to be built. This number is no more than 108.


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

Time limit 1 seconds
Memory limit 128 MiB
Input example #1
Output example #1
Input example #2
Output example #2
Author Анатолий Присяжнюк
Source 2013-2014 2-nd stage All Ukrainian Informatics Olympiad, class 9, Berdichev