#include <bits/stdc++.h>
using namespace std;
int ask(int x) {
    cout << "? " << x << '\n';
    cout.flush();
    int ans;
    cin >> ans;
    return ans;
}
int main() {
    int N;
    cin >> N;
    int st = 1, dr = N, mid;
    while(st <= dr) {
        mid = (st + dr) >> 1;
        int ans = ask(mid);
        if(ans == 0) {
            st = mid + 1;
        } else if(ans == 1) {
            dr = mid - 1;
        } else {
            return 0;
        }
    }
    cout << "! " << st << '\n';
    return 0;
}