Loading of the page to index.php

Good day.
There was a need to make an additional, introductory page before loading with the logo and choice of languages.
Tell me, how can I run a separate executable file like html or php for this, or maybe in the OJS code itself, can I prescribe the boot sequence somewhere?
As an option, I agree to any conditions, except for intervention in the settings of the server on which these files are located.
It is worth OJS
I look forward to hearing!