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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(input())
if n == 1:
	print(1)
	exit(0)
k = 12
ans = k
for i in range(n - 2):
	k = k + 12
	ans += k
print(ans + 1)
