#include <bits/stdc++.h>

typedef long long ll;
typedef unsigned long long ull;

#define FOR(i,a,b) for(int (i)=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define RANGE(vec) (vec).begin(),(vec).end()

using namespace std;


class LengthOfCandle
{
public:
    int ask(int Y){
	cout << "? " << Y << endl;
	int res;
	cin >> res;
	return res;
    }
    void solve(void)
    {
        ll u = 1E+9;
        ll l = 10;

        REP(t,100)
        {
            // X = Y + t
            ll mid = (l+u)/2;
            int res = ask(mid-t);
            if ( res == 0 )
            {
                u = mid;
                break;
            }
            if ( res > 0 )
                l = mid+t;
            else
                u = mid+t;

            if (u == l)
                break;
        }
        cout<<"! "<<u<<endl;
    }
};

#if 1
int main(int argc, char *argv[])
{
        ios::sync_with_stdio(false);
        auto obj = new LengthOfCandle();
        obj->solve();
        delete obj;
        return 0;
}
#endif