Score function

Hello All,
I made a little game like brick breaker.
Now i get 20 points for evry brick i break, and there will be 100 points taken when it hits the bottom.
so when i break 2 bricks i have 40 points, but if i lose a ball by hitting the bottom the score is going to be -60.
How do i prevent this wil become a number below 0, so it will go from 40 to 0 in stead of -60.

Many thanks