Self-adding formula

Hello,

I wonder whether there is a way excel would add a formula to a new column when the new value is added to the adjacent column?

For example:

Columns B:4 and C:4 are now empty. However, when I add value to these columns, a formula from D3 would be automatically added to D4. I know, I can drag formula down, but sometimes I have 100 values and sometimes 50 000 values.

I attach a spreadsheet for the above.

Thank you advance for your assistance on this.

Kind regards,

Jan