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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
#In the name of Allah

from sys import stdin, stdout
input = stdin.readline




a = int(input())
ans = 1
for i in range(1, a):
        ans += 6 * (2 * i)
stdout.write(str(ans))
