Markup languages such as HTML use tags to highlight sections with special significance. In this way, a sentence in boldface can be indicated thus: <B>This is a sentence in boldface</B> Typically every tag has an opening tag of the form <TAG> and a closing tag of the form </TAG>, so that portions of text can be bracketed as above. Tags can then be combined to achieve more than one effect on a particular piece of text simply by nesting them properly, for instance: <CENTER><B>This text is centred and in boldface</B></CENTER> Two of the most common mistakes when tagging text are:  getting the nesting wrong: <B><CENTER>This should be centred boldface, but the tags are wrongly nested</B></CENTER>  forgetting a tag: <B><CENTER>This should be centred boldface, but there is a missing tag</CENTER> Write a program to check that all the tags in a given piece of text (a paragraph) are correctly nested, and that there are no missing or extra tags.