#!/bin/python3

import sys

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

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