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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
import sys


input = lambda: sys.stdin.readline().rstrip()

n = int(input())
print(6*n*(n-1) + 1)