#include <bits/stdc++.h>
    
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
    
mt19937 rng((int) chrono::steady_clock::now().time_since_epoch().count());
    
const int MOD = 1e9 + 7;
const int MAXN = 2e5 + 5;
const int INF = 2e9;

int main () {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    int l = 1, r = n;
    int lst = 0, x;
    while (true) {
        if (r - l <= 3) {
            for (int i = l; i <= r; i++) {
                cout << "? " << i << endl;
                cin >> x;
                if (x == lst) {
                    cout << "! " << i << endl;
                    return 0;
                }
                lst = x;
            }
        }
        int qua = (r - l + 1) / 4;
        cout << "? " << l + qua << endl;
        cin >> x;
        if (x == lst) {
            cout << "! " << l + qua << endl;
            return 0;
        }
        int ant = x;
        cout << "? " << r - qua << endl;
        cin >> x;
        if (x == ant) {
            cout << "! " << r - qua << endl;
            return 0;
        }
        if (x == lst) {
            // vamos pro intervalo do meio
            l += qua + 1;
            r -= qua + 1;
        }
        else {
            // checamos se estamos no primeiro ou no ultimo quarto
            lst = x;
            cout << "? " << l << endl;
            cin >> x;
            if (x == lst) {
                cout << "! " << l << endl;
                return 0;
            }
            ant = x;
            cout << "? " << l + qua - 1 << endl;
            cin >> x;
            if (x == ant && qua > 1) {
                cout << "! " << l + qua - 1 << endl;
                return 0;
            }
            if (x == lst) {
                l++;
                r = l + qua - 2;
            }
            else {
                l = r - qua + 1;
                lst = x;
            }
        }
    }
    return 0;
}