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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 math
import queue

from itertools import permutations

n=int(input())

if n==1:
    print(1)
else:
    print((6*n*(n-1)+1))