#!/bin/python3

import sys

def sumOfGroup(k):
    s=0
    a=(k*(k-1))+1
    for i in range(0,2*k,2):
        s=s+(a+i)
    return(s)
if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)