#include <bits/stdc++.h>

using namespace std;



int main()
{
    int n;
    cin >> n;
    int st = 1, dr = n, p;
    while (st <= dr) {
        int mid = (st +dr) / 2;
        cout << "?" << mid << "\n";
        cout.flush();
        int ans;
        cin >> ans;
        if (ans == 1) {
            dr = mid - 1;
            p = mid;
        }

        else st = mid + 1;
    }
    cout << "!" << p << "\n";
    cout.flush();
    return 0;
}