N = gets.to_i

def query(x, y)
  STDOUT.puts("? #{x} #{y}")
  STDOUT.flush

  gets.to_i
end

(N / 2).times do |i|
  x = 2 * i
  y = 2 * i + 1

  z = query(x, y)

  if z == x
    STDOUT.puts "! #{y}"
    STDOUT.flush
    exit
  elsif z == y
    STDOUT.puts "! #{x}"
    STDOUT.flush
    exit
  end
end

STDOUT.puts "! #{N - 1}"
STDOUT.flush