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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
a = int(input())
i = 1 
c = 1
while (i < a):
	c += 2*i*6
	i += 1
print(c)