How to find the boundary points(most external points) in Hexahedron mesh ？

Hi,

Thanks to all of you for your valuable time and efforts putting in helping others.

I have a Hexahedron mesh.I want to find the  boundary points(most external points) to do next research.

I don't find functions in api,but in hypermesh it has operations(wireframe elements && wireframe elements skin only),which shows in hypermesh it can identify the  boundary points.

If you know how to do this, it will save me a lot of time.I am very grateful for your help!

Thank you very much!!!