Show up a data in a cell when someone enter something

Hi, 

 

I need to enter some information in a different cell (Inventory) and I want the number 1 appear automatically when I put a data.

 

Exemple: 

F4: someone enter "Drill 4", I want de number 1 appear in a hidden cell to addition the number

 

How can I do it? 

Excuse me for writting, I'm french

 

Brondon