#!/bin/python

import sys

def sumOfGroup(k):
      n=(k*(k-1))+1
      ans=n
      for i in range(1,k):
          ans+=(n+2)
          n=n+2
          
      return ans
    # Return the sum of the elements of the k'th group.

if __name__ == "__main__":
    k = int(raw_input().strip())
    answer = sumOfGroup(k)
    print answer