<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=[0]*18258
a[1]=1
n=int(input())
for i in range (2,n+1):
    a[i]=a[i-1] + ((i*2 - 2)*6)

print(a[n])

