! 2019.12.8
!
      program answer
      implicit none
      character(len=100) :: S
      integer :: S_N
      integer :: ans
      integer :: i
      intrinsic len_trim
!
      read(*,*) S
      S_N = len_trim(S)
!
      ans = 0
      do i=1,S_N/2
        if(S(i:i) == S(S_N-i+1:S_N-i+1)) then
        else
          ans = ans+1
        end if
      end do
      write(*,*) ans
      end program answer