def query(y)
  STDOUT.puts("? #{y}")
  STDOUT.flush
  gets.chomp.to_i
end

ok = 0
ng = 10 ** 9 + 1
history = []

100.times do
  y = (ok + ng) / 2
  res = query(y)
  history << res

  if res == 0
    puts [0, y - 1].max
    break
  elsif res < 0
    ok = y
  else
    ng = y

    if (ok - ng).abs <= 1
      ok = [0, ng - 32].max
    end
  end
end