      PROGRAM piyo
      IMPLICIT NONE
      INTEGER,PARAMETER :: p = 16
      integer(p) :: i,ans, l
      character(2*10**5) :: s,t
      
      read*,s
      read*,t
      
      l = len_trim( s )
      
      ans = 0
      do i = 1,l
        if( s(i:i)/=t(i:i) )then
          ans = ans + 1
        end if
      end do
      
      print'(i0)',ans
      
      
      stop
      !debugg
      
      
      
      END PROGRAM