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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
def init():
    a = int(raw_input())
    return int(a)

def solve(n):
    a = (3 * n - 2) * (3 * n - 1) / 2
    b = 3 * n * (n - 1) + 1
    return 2 * a - b

if __name__ == "__main__":
    a = init()
    print solve(a)
