Handwriting Keynote or PowerPoint from iPad

I am a teacher and need to be able to produce handwritten content in volume, fast for my lessons. As I teach Maths, typing everything up in advance is to time consuming. During the lesson I can stand at the interactive whitboard and write on the board during the lesson. All my hand written content has been written using the proprietry software that comes with the interactive whitreboard. Trouble is, as soon as I go to a different room with a different type of interactive white board my content is useless as we can't transfer the file to the new platform.

Recently, Microsoft has introduced the pen annotation tool into PowerPoint so I can now hand write slides (not the screen show which has had a pen tool for a whilte). Is there any way anyone knows of handwriting using an ipad app directly into either Powerpoint or Keynote. My school provides me with an iPad and I have my lesson plannign software on it. If I could find a way of producing my content, which is very basic, in an efficient and quick way it would be great.

Any help or pointers welcome. I'm happy to buy an app to do this but it must offer a slick way of getting content quickly into either Powerpoint of Keynote. Alternativly, does anyone know of a whiteboard app which will allow me to product multiple pages of written content with an export to keynote / powerpoint function on it without having to go via pdf?

Cheers

Mark