HS08 - ATM

New to CodeChef. I tried out a problem.
Here’s the Problem: https://www.codechef.com/problems/HS08TEST
My submission:

x, bal = map(float,input().split())
if x%5==0 and bal > x+0.50:
    bal -= x+0.50

but on submitting it says wrong answer. Please point out my mistake.

bal >= x+0.50
As the balance can be equal to zero after the transaction.