Using max() function with entity framework throws an exception

So I need to get the max value of a column (or the last one) using entity framework and both of these queries throw exceptions:

(The ID I'm trying to retrieve is of type varchar, but it works in raw sql, I think it should work here too)

This one:

string maxCurrentID = db.reservations.Max().ReservationID;

Throws this:

The specified method 'EntityClub_.reservacion Maxreservacion' on the type 'System.Linq.Queryable' cannot be translated into a LINQ to Entities store expression because no overload matches the passed arguments.

and this one:

 string maxCurrentID = db.reservations.LastOrDefault().ReservationID;

LINQ to Entities does not recognize the method 'EntityClub_.reservacion LastOrDefaultreservacion' method, and this method cannot be translated into a store expression.

How can I obtain the expected values?