What to write in a MLA format page header, if the work is a collaborative one?

As shown in the image below (upper right corner), we must put a surname before the page number according to MLA format guidelines. However, I am now working on a document that I and two others have collaboratively produced. We all put in the same amount of effort, so I cannot just put one name on there.

Do I just put three surnames before the page number? Should I just randomly choose one person’s name? Or can I not put any name before the page number?