program minor

 implicit none
 character::s*200000,t*200000,ss*200000,tt*200000
 integer::length,i,ans

 read*,s,t
 length=len_trim(s)
 !print*,length
 !ss=s(1:length)
 !tt=t(1:length)
 !print*,s,t


 ans=0
 do i=1,length
  if(s(i:i)/=t(i:i)) then
   ans=ans+1
  end if
 end do

 print*,ans

end program minor