#include <bits/stdc++.h>

using namespace std;

namespace {

    typedef double real;
    typedef long long ll;

    template<class T> ostream& operator<<(ostream& os, const vector<T>& vs) {
        if (vs.empty()) return os << "[]";
        os << "[" << vs[0];
        for (int i = 1; i < vs.size(); i++) os << " " << vs[i];
        return os << "]";
    }
    template<class T> istream& operator>>(istream& is, vector<T>& vs) {
        for (auto it = vs.begin(); it != vs.end(); it++) is >> *it;
        return is;
    }

    void solve() {
        int lb = 1, ub = int(1e9 + 1);
        while (lb + 1 < ub) {
            int mid = (lb + ub) / 2;
            cout << "?" << mid << endl;
            string buf; getline(cin, buf);
            if (buf[1] == '0') {
                ub = mid;
            } else {
                lb = mid;
            }
        }
        cout << lb << endl;
    }
}

int main() {
    solve();
    return 0;
}