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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())

sum = (12 + 12*(n-1)) * (n - 2 + 1) / 2

print sum + 1
