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

Source: codeforces | Difficulty: MEDIUM
Tags: Implementation


Solutions: