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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

a = input()
s = 1
if a == 1: print s; sys.exit(0)
for i in range(2,a+1):
    s += 6*(i-1)*2 
print s