<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
n=int(input())

a=3*n-2
b=n-1
print(int((a*(a+1))/2 + ((b*(b+1))/2)*3))