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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 star(n):
    f = 1
    while n:
        n -=1
        f += n*12
    return f

print(star(int(input())))