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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=input()
n=n-1
if n==0:
	print "1"
	exit(0)
print (n*(2*12+(n-1)*12))/2+1
