I need to implement an application that will be installed on multiple PCs. These apps need to read/write a single file on a server (which is not mine). The problem I am facing is simultaneous access to this file. The file is not necessarily a file, it is a resource, an int value, which each app will increment an bring to a maximum after which the first app to find it over the maximum value will reset it to 0. Any ideas as to how to store this value on the server and how to access it will be very helpful. Thanks in advance.

P.S. Because the server isn't mine (it's paid-for web hosting) I don't think server side code is an option. I also already have all the apps reading files from the server but each app has it's own http location so no simultaneous access happening there.