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

res = query(100)

if res == 0
  puts 100
  exit
elsif res < 0
  ok = 0
  ng = 100
else
  ok = 100
  ng = 10 ** 9 + 1
end

99.times do |i|
  y = (ok + ng) / 2
  res = query(y)

  if res == 0
    STDOUT.puts(y + i + 1)
    STDOUT.flush
    break
  elsif res < 0
    ng = y
    ok = [0, ok - 1].max
  else
    ok = [0, y - 1].max
  end
end