#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    res=(((k*(k-1))/2)*2)+1
    count=0
    x=res
    while count<(k-1):
        x+=2
        res+=x
        count+=1
    return res

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