program abc37
 implicit none
 character(len=2*10**5)::T,S
 integer::c=0,L,i
 read(*,*)S
 read(*,*)T
 L=len_trim(S)
 do i=1,L
  if(S(i:i)/=T(i:i))then
   c=c+1
  end if
 end do
 print'(i0)',c
end program abc37