      PROGRAM PalindromePhilia
      IMPLICIT NONE
      character(100) :: s
      integer :: l,h,i,ans
      
      read*,s
      l = len_trim( s )
      
      h = l /2
      ans = 0
      do i = 1,h
        if( s(i:i)/=s(l-i+1:l-i+1) )then
          ans = ans + 1
        end if
      end do
      
      print*,ans
      
      
      
      END PROGRAM