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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
# -*- coding: utf-8 -*-

a = int(raw_input())

def f(n):
    return (2*n-1)*3 + (2*n-3)*3

res = 1
for i in xrange(2, a+1):
    res += f(i)
print res
