program sample
    implicit none
  
    integer(8) :: i,j,m,n
    character(len=200000)::s,t
    integer(8),allocatable :: x(:),y(:)
  
    read(*,*)s
    read(*,*)t
    n=len_trim(s)
    m=0
    do i=1,n
        if(s(i:i) .ne. t(i:i))then
            m=m+1
        end if
    end do
    write(*,*) m
  
    stop
end program sample
  

