# frozen_string_literal: true

left = 1
right = 10**9

loop do
  if left == right
    puts %(! #{left})
    STDOUT.flush
    exit
  end

  center = (left + right) / 2 + 1
  puts %(? #{center})
  STDOUT.flush
  gets.chomp == '1' ? (left = center) : (right = center - 1)
end