<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
def f(x):
     return 6 + 6*(2*x + 1)

a = int(raw_input())
sum = 1
for x in xrange(a-1):
     sum += f(x)

print sum

     

