Hive

Time limit2sMemory limit1024 MB

Summary

Given the size n of a hexagonal hive built from rings around one center cell, print the total number of cells.

Level: Easy2 of 10
Topics: Math, Implementation
Solved: No attempts yet

Statement

Kevin works as a builder. Since Kevin is a bee, he builds only beehives.

A beehive is made of identical cells, each one a regular hexagon. Among bees, a hive of size one is a hive made of a single cell. A hive of size two is a hive of size one surrounded by one ring of cells. In general, a hive of size $k$ is a hive of size $k-1$ surrounded by a ring of cells.

Recently Kevin was asked to build a hive of size $n$ . To plan the work, he needs the exact number of cells in the hive. Write a program that takes the size $n$ and prints the number of cells in that hive.

Input

The input file contains a single integer $n$ ( $1 \le n \le 10^9$ ), the size of the hive.

Output

Print a single number, the number of cells in the hive.

Examples2

Example 1
Input
```
1
```
Expected output
```
1
```
Example 2
Input
```
3
```
Expected output
```
19
```