try:
inputs = input()
input1 = float(inputs.split()[0])
input2 = float(inputs.split()[1])
if input1>0 and input1<=2000 and input2>=0 and input2<=2000:
if input1+0.5<input2 and input1%5==0:
print(input2-input1-0.50)
else:
print(input2)
except EOFError:
pass