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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
n = int(input())
m = n-1
n = 1+3*m
print(n*(n+1)//2 + 3*(m*(m+1)//2))