#include <bits/stdc++.h>
using i64 = long long;
const i64 INF = 1e18;

void solve()
{
    int st = 1, dr = 1e9;
    std::cin >> dr;
    int rez = 0;
    while (st <= dr) {
        int mid = (st + dr) / 2;
        std::cout << "? " << mid << std::endl;
        int response;
        std::cin >> response;
        assert(response != -1);
        if (response == 1) {
            dr = mid - 1;
            rez = mid;
        } else {
            st = mid + 1;
        }
    }
    std::cout << "! " << rez << std::endl;
}
signed main(void)
{
    //freopen("podm.in", "r", stdin);
    //freopen("podm.out", "w", stdout);
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    int tt = 1;
    while (tt--) {
        solve();
    }
}