How Do I Have my Program Accept a Negative Year as Valid

I am creating a time calculator game to learn how to code and am running into trouble when I input a negative year. How can I program a time calculator that recognizes this negative year as BCE while not displaying an invalid message? I

Answer 1

[Alexander]

datetime(-1,1,1) answeres 01-Jan--0001 which is correct.

[CHRISTY]

Thank you, how would I do this for the MM/DD/YYYY format where the user enteres their date like this?

[Walter Roberson]

datetime('01/01/-0001', 'inputformat', 'MM/dd/uuuu')

ans = datetime
   01-Jan--0001