I need a math function for an RPG

3absh

Basically the enemies increase 1 HP for every 10 days in the first 100 days then start increasing by 2 HP every 10 days the next 200 days, and 3HP every 10 days for the next 300 days and so on.

How can I write this as an expression?

tatiang

When mod(game.day,10)=0 AND game.day>0
     game.hp=game.hp+floor(game.day/100)+1