#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    ind=(k-1)*(k)/2
    odds=0
    for i in range(ind,ind+k):
        odds+= 2*i+1
        
    return odds
if __name__ == "__main__":
    k = int(raw_input().strip())
    answer = sumOfGroup(k)
    print answer