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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 c(n): 
    r = 1
    while n > 1:
        n -= 1
        r += n * 12
    return r
print c(int(raw_input()))
