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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 starNumber(n):
    star = [0] * n
    star[0] = 1
    for i in range(1, n):
        star[i] = star[i - 1] + 12 * (i + 1) - 12
    return star[n - 1]
n = int(input())
print(starNumber(n))
