Week1 = str(input())
Week2 = str(input())

CircleNumOfWeek1 = Week1.count("〇")
CircleNumOfWeek2 = Week2.count("〇")

if(CircleNumOfWeek1 >= CircleNumOfWeek2):
    print(CircleNumOfWeek1)
elif(CircleNumOfWeek2 >= CircleNumOfWeek1):
    print(CircleNumOfWeek2)
else:
    print(CircleNumOfWeek1)