<image>

Input

The input contains a single integer a (1 ≤ a ≤ 18257).

Output

Print a single integer output (1 ≤ output ≤ 2·109).

Examples

Input

2


Output

13
k = int(raw_input())
print sum((i + 1) * 6 + (i - 1) * 6 for i in xrange(k)) + 1
