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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
n=int(input())
sum = 1
if(n==1):
    print(sum)
else:
  for i in range(n-1):
    sum += 12*(n-1)
    n=n-1
  print(sum)