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

int main() {
    long long N;
    cin >> N;

    long long st = 1, dr = N;

    while (st < dr) {
        long long mid = (st + dr) / 2;

        cout << "? " << mid << endl;
        cout.flush();

        int ans;
        cin >> ans;

        if (ans == -1) return 0;

        if (ans == 0)
            st = mid + 1;
        else
            dr = mid;
    }

    cout << "! " << st << endl;
    cout.flush();

    return 0;
}