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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
#!/usr/bin/python2

a = int(raw_input())

ans = sum(range(a, a + a)) + sum(range(a, a + a - 1))

ans += sum(range(1, a)) * 6

print ans