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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
num = int(input())
if num == 1:
    print("1")
else:
    print(int((num-1)*(num)/2)*12+1)
