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