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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
from math import *
a= int(raw_input())

ans=1

for i in range(2,2*a,2):
    ans+=6*i

print ans
