#include <iostream>
using namespace std;
 
int ask(int Y){
    cout << "? " << Y << endl;
    int res;
    cin >> res;
    return res;
}
 
int solve(){
	if(ask(40) <= 0){
    	for(int i=1;;i++){
			if(ask(0) == 0){
				return i;
			}
    	}
	}
    // [lo, hi]
    int lo = 40, hi = 1e9 - 1;
    for(int askCount=1;;++askCount){
        int mid = (lo + hi) / 2;
        int res = ask(mid);
        if(res == 0){
            return mid + askCount;
        }
        if(res < 0){
            hi = mid - 1;
        } else {
            lo = mid + 1;
        }
        if(lo == hi){
            return lo + askCount;
        }
        --lo;
        --hi;
    }
    return -1;
}
 
int main(){
    int Y = solve();
    cout << "! " << Y << endl;
    return 0;
}