#!/bin/python3

import sys

def sumOfGroup(k):
    a=((k)*(k-1))//2
    an=1+(a)*2
    #print(an)
    ann=1+(a+k-1)*2
    
    s=k*(an+ann)
    s=s//2
    return s
    #print(a)
     
    #return s    
    
    # Return the sum of the elements of the k'th group.

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