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

ok = 0
ng = 10 ** 9 + 1

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

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