N = gets.to_i

def send_query(k)
  STDOUT.puts("? #{k}")
  STDOUT.flush

  gets.to_i
end

l = 1
r = N + 1

20.times do
  k = (l + r) / 2
  s = send_query(k)

  if k.even? && s == k / 2
    r = k
    break
  elsif s <= k / 2
    l = k
  else
    r = k
  end
end

puts "! 1 #{r}"