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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
k = int(raw_input())
sum = ans = 0

for i in xrange(k - 1):
    sum += 12
    ans += sum
print ans + 1
