How to calculate the slide size to fit the shape using C#?

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C#

VSTO

PowerPoint

VS2013

Hi,
I am using Visual studio 2013 Powerpoint to create Index slide which contains all the slide titles and subtitles as a shape group (i.e) Instead of table i am using textbox to store each of the slide titles, slide number and subtitles separately and then I am grouping the text box so that a shape group holds details of one slide.But the shape will not be created using code and it will be a part of a presentation and we want to copy the shape to add the details.

My problem is as the user can have any kind of shape and size. so I have to copy the shape and fit into the slide
so i need to calculate the size of the slide and size of the shape and to fit it. but I don't know how to calculate.

Can any one please help me?
note:
I am copying the shape and pasting it by creating an new slide as:
PowerPoint.ShapeRange pstgrp=Globals.ThisAddIn.Application.ActivePresentation.Slides[agendaSlideNo].Shapes.Paste();

agendaSlideNo is to get the agenda slide number to which shapes to be pasted.

thanks in advance!!