#include <iostream>
using namespace std;
int n, k, q;
int main()
{
    cin >> n;
    int st = 1, dr = n;
    while (st <= dr) {
        int k = (st + dr) / 2;
        if (st == dr)
        {
            cout << "! " << k << '\n';
            cout.flush();
            return 0;
        }
        cout << "? " << k << '\n';
        cout.flush();
        cin >> q;
        switch (q) {
        case 0:
            st = k + 1;
            break;
        case 1:
            dr = k;
            break;
        }
    }
}