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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
import math
t=int(input())
if(t==1):
    print(1)
else:
    x=t-1
    print(6*t*x +1)
