s = gets.strip.split("")

c = s.size / 2
count = 0
if s.size.even?
   for x in (0..c)
      unless s[x] == s[s.size - x - 1]
         s[s.size - x - 1] = s[x]
         count += 1
      end
   end
else
   for x in (0..c)
      unless s[x] == s[s.size - x - 1]
         s[s.size - x - 1] = s[x]
         count += 1
      end
   end
end

puts count
