Flag the inappropriate content and not allowing people to add a content? I have added a content type called "share", I have given the user permissions for this content type, meaning he can add the content and he can share to any one..

If any user feels that the content is inappropriate, he can flag the content accordingly.  If a piece of content is flagged 3 times, the content is automatically unpublished.. I have done this using the Rules module...

But here what I want is if a user's content is unpublished as "inappropriate", the next time he should not be able to post any content but he can still access the site.

How can I accomplish this?
I would look into using rules again.

You are going to need a way of identifying users who should not be able to post. Set a rule to apply a flag to the users account once one of their nodes has been flagged 3 times. 

Then use this flag in another rule as an IF to only apply it to said user, then maybe either redirect the users who access node/add pages to a page with a custom warning message or try another form of disabling the node creation. Please see below


  Event:
  Content going to be saved / Accessing a page
  
  Conditions:
  User is flagged with "suspended user"
  
  Actions:
  Page Redirect
  Show a message on the site


EDIT: Am I correct in assuming you are wanting users to flag a node inappropriate? You should be able to use something like the rule you have already created to do so, just also flag the node author when you flag the content...