Even numbers series

I'm trying to create a program that generates a series and asks the user to enter the last number in it.
I wrote it but the output should be something similar to

The Sum= -2+4-6+8-10+12-14+16-18+20....

And my output is

-20-18-16-14-12-10-8-6-4-2

So, as you can see, I have three mistakes which are

1. Their sequence(should start from 2 not vice versa)


2. The signs, it should be one time - and another + but I have no clue how


3. Writing sum once at the beginning of the series :(

Here's my code

import java.util.*;
 public class Even{
 public static void main (String [] args){
 Scanner myScanner= new Scanner(System.in);
 System.out.println("Enter last number");
 int lastNumber= myScanner.nextInt();
 if (lastNumber<=1)
            {
             System.out.print("error");
         }
 while(lastNumber>1){
             System.out.print("-"+lastNumber);
             lastNumber-=2;
         }
     }
 }
 

Thanks in advance!

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