#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <iostream>
#include <vector>
#include <string>
#include <sstream>
#include <algorithm>
#include <utility>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <functional>

using namespace std;

#define fst first
#define scd second
#define PB push_back
#define MP make_pair
#define size(a) ((int)a.size())
#define int long long
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define omajinai ios::sync_with_stdio(false);cin.tie(0)

typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> pii;
typedef vector<pii> vpii;

template<typename T>T& max(T&a,T&b){if(a>=b)return a;return b;}
template<typename T>T& min(T&a,T&b){if(a<b)return a;return b;}
template<typename T>bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<typename T>bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}
template<typename T>T get(){T a;cin>>a;return a;}
template<typename T>T rev(T a){reverse(all(a));return a;}
template<typename T>vector<T>&sort(vector<T>&a){sort(all(a));return a;}

const int inf = 1e9;
const ll linf = 3e18;
const double eps = 1e-9;

signed main()
{
    int lb = 0, ub = 1e9;

    for (int i = 0; i < 60; ++i) {
        if (ub - lb <= 3) break;
        int mid = (lb + ub) / 2;
        cout << "? " << mid << endl;

        int res; cin >> res;

        if (res == 0) {
            cout << mid << endl;
            return 0;
        } else if (res == -1) {
            ub = mid;
            lb = min(lb - 1, max(lb, 0ll));
        } else if (res == 1) {
            lb = mid;
        }
    }

    lb -= 5;
    for (int i = 0; i < 10; ++i) {
        cout << "? " << lb << endl;
        int res; cin >> res;
        if (res == 0) {
            cout << lb << endl;
            return 0;
        }
    }
}