等差数列

 1 import java.util.*;
 2  
 3 public class Main{  
 4     public static void main(String[] args){
 5         Scanner sc = new Scanner(System.in);
 6         while(sc.hasNext()){
 7             int N = sc.nextInt();
 8             int sum = 0;
 9             sum = (2+3*N-1)*N/2;
10             System.out.println(sum);
11         }
12     }
13 }