#include <bits/stdc++.h>

using namespace std;
 
#ifdef LOCAL
#include "debug.h"
#else
#define dbg(...) 69
#define nl(...) 42
#endif

#define ll long long
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ll random(ll st, ll dr) {
    assert(st <= dr);
    return st + rng() % (dr - st + 1);
}

const int MOD = 1e9 + 7;
const int N = 2e5 + 10;

int ask(int x) {
    cout << "? " << x << endl;
    int p;
    cin >> p;
    return p;
} 

void solve(int test, istream &cin, ostream &cout) {
    int n;
    cin >> n;
    int st = 1;
    int dr = n;
    
    while (st <= dr) {
        int mid = st + (dr - st) / 2;
        int q = ask(mid);

        if (q == 1) {
            st = mid + 1;
        } else {
            dr = mid - 1;
        }
    }

    cout << "! " << dr << endl;
}

int main() {
    // ifstream cin("tst.in");
    // ofstream cout("tst.out");
    ios_base::sync_with_stdio(0);
    cin.tie(NULL);
    auto start = std::chrono::high_resolution_clock::now();

    bool multiTest = false;

    int t;    
    if (multiTest) {
        cin >> t;
    } else {
        t = 1;
    }

    for (int test = 1; test <= t; test++) {
        solve(test, cin, cout);
    }

    auto stop = std::chrono::high_resolution_clock::now();
    auto duration = std::chrono::duration_cast<std::chrono::microseconds>(stop - start);
    // cerr << fixed << setprecision(6) << "Running time: " << (double) duration.count() / 1e6 << " seconds" << '\n';

    return 0;
}