#!/bin/python

import sys

def sumOfGroup(k):
    x=k-1
    m=(x**2)+(x+1)
    l=[]
    for i in range(0,k):
        l.append(m)
        m+=2
    return sum(l)
        
    # Return the sum of the elements of the k'th group.

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