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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 = 1
for x in range(2,a+1):
    c += x + 10*(x-1) + x-2
print c