# coding: utf-8
#ABC122B_ATCoder.rb
str = gets.chomp
flag = 0
max = 0

acgt = ["A","C","G","T",""]
acgt.each do |s1|
  acgt.each do |s2|
    acgt.each do |s3|
      acgt.each do |s4|
        acgt.each do |s5|
          ss = s1+s2+s3+s4+s5
          if str.include?(ss)
            if ss.size > max
              max = ss.size
            end
          end
        end
      end
    end
  end
end
puts max

