export seleted as dwg at certain frames.

I would appreciator it if someone can help me to write a script that let me export selected objects as dwg at certain frames.
Ideally have an input so the user can enter specific key frames like 1,4,6,25,99
and script takes this input and export selected objects as dwg files and give me file1.dwg file4.dwg file6.dwg file25.dwg and file99.dwg.
and each of these dwg files contain my selected objects at that particular frame.
Thanks for your help.