#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    p=(k*(k-1))+1
    ans=0
    for x in range(0,k):
        ans=ans+p+(2*x)
        
    return ans    
    

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