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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=input()
c=0
b=1
for i in range (a-1):
   b+=6*(i+2)+c
   c=6*(i+1)
print b
