S = gets.chomp
N = S.size
M = N / 2

if S != S.reverse
  puts N
  exit
end

if S.size == 1
  puts -1
  exit
end

counter = Hash.new(0)

M.times do |i|
  s = S[i]
  counter[s] += 1
end

if N.even?
  if counter.size == 1
    puts 0
  else
    puts N - 2
  end
else
  if counter.size == 1
    puts -1
  else
    puts N - 2
  end
end