#!/bin/python3

import sys

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

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