House of Cards

Yūko and Mio are building a house of cards.

A house has $N$ stories, where $N$ is a whole number.

Each story is made out of struts, which may be supported by platforms.

• The top story has 2 struts and 1 platform.
• The second-to-top story has 4 struts and 2 platforms.
• The third-to-top story has 6 struts and 3 platforms.

In general, each story has 2 more struts and 1 more platform than the story above it.

Note that the bottom story does not have a platform, because the table is already supporting it.

How many cards are needed to build a house with $N$ stories?

Input

Input is an integer, $0 < N \le 10{,}000$, which is the number of stories.

Output

Output an integer, $K$, the number of cards needed to build a house with $N$ stories.

Example

This house has 4 stories. There are 2 + 4 + 6 + 8 = 20 struts and 1 + 2 + 3 = 6 platforms in this house.

This adds up to 20 + 6 = 26 cards.