program b172

implicit none
character(len=200000) :: s, t
integer :: i, x

x = 0

read *, s
read *, t

do i =1, 200000
 if (s(i:i) == ' ') then
  exit
 else if (s(i:i) == t(i:i)) then
  x = x
 else
  x = x + 1
 end if 
end do

print *, x

end program b172