题解 | #等差数列#

import java.util.*;

public class HJ100 {
    public static void main() {
        Scanner in = new Scanner(System.in);
        while(in.hasNext()) {
            int sum=0;
            int size = in.nextInt();
            int[] nums = new int[size];
            int n=2;
            for(int i=0,y=0;i<size;i++) {
                nums[i]=n+(3*y);
                y++;
            }
            for(int num : nums) {
                sum+=num;
            }
            System.out.println(sum);
        }
    }
}