south = str(input())
north = str(input())
lst1 = list(south)
lst2 = list(north)
counter = 0
i = 0

while (len(lst1) != 0 or len(lst2) != 0):
    if len(lst1) == 0 or len(lst2) == 0 or lst1[i] == lst2[i] == 'L':
        lst1 = lst1[1:]
        lst2 = lst2[1:]
    elif (lst1[i] == 'L') & (lst2[i] != 'L'):
        lst2 = lst2[1:]
    elif (lst2[i] == 'L') & (lst1[i] != 'L'):
        lst1 = lst1[1:]
    else:
        lst1 = lst1[1:]
        lst2 = lst2[1:]
    counter += 1
counter += len(lst1) + len(lst2)
print(counter)