# 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|
          acgt.each do |s6|
            acgt.each do |s7|
              acgt.each do |s8|
                acgt.each do |s9|
                  acgt.each do |s10|
                    ss = s1+s2+s3+s4+s5+s6+s7+s8+s9+s10
                    if str.include?(ss)
                      if ss.size > max
                        max = ss.size
                      end
                    end
                  end
                end
              end
            end
          end
        end
      end
    end
  end
end
puts max

