Addition and Subtraction Program

I am making a program that adds and subtracts numbers. I need to be able to get the leading sign to be recognized, but this is causing problems. When I have a space between the leading sign and the leading number (- 2 - 3) it is not working, but when I have no space (-2 - 3) it is working. How do I solve this problem. Here is the code, and thanks for the help!

Java Code:

import java.io.*;
import java.util.*;
public class Tester
{
    public static void main(String args[])
    {
        Scanner kb = new Scanner(System.in);
        
        System.out.print("Enter something like 8 + 33 + 1,345 + 137  :  ");
        String s = kb.nextLine();
        
        Scanner sc = new Scanner(s);
        
        sc.useDelimiter("\\s+");
        
        String operation;
        int num;
        int sum = 0;
        int count = 0;
        operation = "";
        char ch = s.charAt(0); 
        
        while(sc.hasNextInt( ))
        {
         
         if(!(Character.isDigit(ch)))
         {
             operation = sc.next();
         }
         num = sc.nextInt();
        if (count == 0)
        {
            sum = sum + num;
        }
        else if (operation.contains( "+" ))
        {
            sum = sum + num;
        }
        else if (operation.contains("-"))
        {
            sum = sum - num;
        }
               if(sc.hasNext())
        {
            operation = sc.next();
        }
        count++;
        }
        System.out.println("Sum is: " + sum);
}
}