Fatal error: Uncaught Error: Undefined constant "first_number" in /in/Y0Itf:5
Stack trace:
#0 {main}
thrown in /in/Y0Itf on line 5
Process exited with code 255.
Warning: Use of undefined constant first_number - assumed 'first_number' (this will throw an Error in a future version of PHP) in /in/Y0Itf on line 5
first_number