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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
#!/usr/bin/env python

from sys import stdin

N = int(stdin.readline())

#N -= 1
res = 1 + 12 * (N * (N-1)) / 2
print res
