Please help with insert a semicolon at the end!

Hey everyone. I recently had this compiler error:

UCE0001: ';' expected. Insert a semicolon at the end.

After doing some research, I realized that the problem was not necessarily in the semicolon, but in the script itself. I went over it for a while, but couldn't find any possible erros. Here's the script:

 using UnityEngine.SceneManagement;
 
 function OnGUI ()
 {
     if(GUI.Button (Rect (500, 100, 100, 50), "Play"))
     {
         SceneManager.LoadScene(1);
     }
 }

Does anyone see anything I'm missing?