import System.IO
import Data.List

main = main' 1 (10^9)

main' lo hi
 | succ lo == hi = putStrLn ("! " ++ show lo)
 | otherwise = do
  let md = div (lo + hi) 2
  putStrLn ("? " ++ show md)
  hFlush stdout
  ack <- readLn
  if ack == 0 then main' lo md else main' md hi