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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
sum = 1
n = int(input())
if n ==1:
    print(sum)
else:
    for i in range(1, n):
        sum += 12*i
    print(sum)

