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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
a = int(input())
k = 1
p = 12
for i in range(a - 1):
    k += p
    p += 12
print(k)