Does anyone have any suggestions on how to do this trick in excel?

Within the cell A1, B1, C1, when I enter a number in one of three cell, such
as 3 in cell A1, then 3 will be automatically display on cell B1 and C1. On
the next step, if I enter 6 in cell B1, then 6 will be automatically display
on cell A1 and C1. On the next step, if I enter 8 in cell C1, then 8 will be
automatically display on cell A1 and B1.
Does anyone have any suggestions on how to do this trick in excel?
Thanks in advance for any suggestions
Eric