#include <bits/stdc++.h>
using namespace std;

using ll = long long;

class Solver {
  public:
    bool solve() {
        ll l = 0, r = 1e10;
        int cnt = 90;
        while(cnt--) {
            ll m = (l + r) / 2;
            cout << "? " << m << endl;
            cout.flush();
            
            int res; cin >> res;
            if(res > 0) l = m;
            if(res < 0) {
                r = m;
                if(l > 0) l--;
            }
            if(res == 0) {
                cout << "! " << max(m - 1, 0LL) << endl;                
                exit(0);
            }
        }
        cout << "! " << l << endl;
        
        return 0;
    }
};

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    Solver s;
    s.solve();
    return 0;
}