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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
n = int(raw_input())
c = 1
for i in xrange(n):
    c += 12 * i
print c
#print (12 ** (n + 1) - 1) / (12 ** n - 1)