import std.stdio;

void main(){
	auto numMin=1;
	auto numMax=1000000001;
	for(;;){
		int chkNum=(numMin+numMax)/2;
		writefln("? %d",chkNum);
		if(readln()[0..$-1]=="1") numMin=chkNum; else numMax=chkNum;
		if(numMin==numMax-1){
			writefln("! %d",numMin);
			break;
		}
	}
}