int = gets.to_s
int_size = int.length
half_size = (int.length / 2)

front = int[0, half_size]
back = int[half_size, int.length - 1]

counts = 0

half_size.times do |n|
  if front[n] != back.reverse[n]
    counts += 1
  end
end

p counts
