#include<iostream>

using namespace std;

int main(){

	long long min=1,max=1000000000;
	bool ans;

	while(min<max-1){
		long long mid=(max+min)/2;
		cout<<"? "<<mid<<endl<<flush;
		cin>>ans;
		if(ans) min=mid;
		else max=mid;
	}
	cout<<min<<endl;
}