171_B. Star
<image>

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
```python
def star(n):
    a, b = 1, 12
    for i in range(2, n + 1):
        a += b
        b += 12
    return a


print(star(int(input())))

```