(let (
	(numMin 10)
	(numMax 1000000001)
)
	(call/cc(lambda(return)(let loop((turn 0))
		(let ((chkNum (if(= 0 turn) 100 (floor(/(+ numMin numMax) 2)))))
			(format #T "? ~d~%" chkNum)(flush)
			(let ((chk (read-line)))
				(if(string=? "1" chk) (set! numMin chkNum)
				(if(string=? "-1" chk) (set! numMax chkNum)
				(begin
					(format #T "! ~d~%" (+ chkNum turn))(flush)
					(return)
				)))
				(when(< 0 numMin) (set! numMin (- numMin 1)))
				(set! numMax (- numMax 1))
				(loop (+ 1 turn))
			)
		)
	)))
)