Avoid concurrent users accesssing the same webpage asp.net

<div>I have a web application with master  data entry pages to be created. there are some 500 users can access and input master data.</div> <div></div> <div>I want to prevent the user enter into the same web page, when one user is already accessing the page.</div> <div></div> <div>i.e. Avoid concurrent users accessing the same web page.</div>