<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=[0]*n
a[0]=1
for i in range(1,n):
    a[i]=a[i-1]+(6*(i*2))
print(a[n-1])
