ATM Problem| I am getting wrong answer. why?

I am getting all the outputs correctly as mentioned in the question. Still after submitting I am getting wrong answer. Why?
link : Contest Page | CodeChef

a,b = map(float,input().split())
if a > b or a%5 != 0 :
print(format(b,".2f"))
else:
ans = (b-a - 0.50)
print(format(ans,".2f"))