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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
import copy
from collections import Counter
sys.setrecursionlimit(11111)
import re
import itertools

n = int(sys.stdin.readline().strip())
print 6 * n * (n-1) + 1