<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
a = int(input())
ans = 1
z = 0
for i in range(2, a + 1):
    z += 2
    ans += z * 6
print(ans)