cs8025 Parsing Error

I just began learning how to use Unity today with a course on Udemy. I did exactly as the person did (using Gui to make a cube move) when coding but I keep getting the same error. This is my first time and I am trying not to miss anything!

 using UnityEngine;
 using System.Collections;
 
 public class ForceScript : MonoBehaviour {
 
     public Rigidbody mycube;
 
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 
     void OnGUI() {
         if (GUI.Button(new Rect(10, 10, 150, 100), "Upward Force")){
             mycube.AddForce (0,200F,0);
     }
 }

I'll be looking forward to a response. Thanks.