local n = io.read("*n", "*l")
for i = 0, n - 2, 2 do
  io.write("? " .. i .. " " .. i + 1 .. "\n")
  io.flush()
  local ans = io.read("*n", "*l")
  if ans == i then
    io.write("! " .. i + 1 .. "\n")
    io.flush()
    os.exit()
  elseif ans == i + 1 then
    io.write("! " .. i .. "\n")
    io.flush()
    os.exit()
  end
end
io.write("! " .. n - 1 .. "\n")
io.flush()