#!/bin/python

import sys

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

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