import java.util.Scanner;
class Sumofodd{
public static void main(String[]args){
Scanner sc =new Scanner(System.in);
long K=sc.nextInt();
    long n=(K-1)*K/2;
    long c=2*n-1;
    long sum=0;
    for(long i=1;i<=K;i++)
    {
        c=c+2;
        sum=sum+c;
    }
    System.out.println(sum);
}
}