A. Crystal Ball Sequence
time limit per test
2 seconds
memory limit per test
256 megabytes
input
stdin
output
stdout

Crystal ball sequence on hexagonal lattice is defined as follows: n-th element is the number of lattice points inside a hexagon with (n + 1) points on each side. The formula is Hn = 3·n·(n + 1) + 1. You are given n; calculate n-th element of the sequence.

Input

The only line of input contains an integer n (0 ≤ n ≤ 9).

Output

Output the n-th element of crystal ball sequence.

Examples
Input
1
Output
7
Input
3
Output
37