#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
int solve() {
    int n; cin >> n;
    auto query = [](int x) -> int {
        cout << "? " << x << endl;
        cin >> x;
        return x;
    };
    tree<int, null_type, less<>, rb_tree_tag, tree_order_statistics_node_update> tr;
    // auto insert = [&tr](int x) -> void {tr.insert(x); };
    for (int i = 1; i <= n; ++i) tr.insert(i);
    auto rank = [&tr](int x) -> int {return tr.order_of_key(x); };
    auto erase = [&](auto bg, auto ed) -> void {
        for (; bg != ed;)
            tr.erase(bg++);
    };
    auto get = [&tr]()->array<decltype(tr.begin()), 2> {
        int x = tr.size() / 4;
        auto lt = tr.find_by_order(x), rt = tr.find_by_order(tr.size() - 1 - x);
        return { lt,rt };
    };
    // auto before = [&](int x) -> int {
    //     int lft = rank(x);
    //     int rgt = tr.size() - 1 - lft;
    //     // cerr << "lft = " << lft << " rgt = " << rgt << endl;
    //     lft = x - 1 - lft;
    //     rgt = n - x - rgt;
    //     return abs(lft - rgt);
    // };
    int lst = 0;
    while (tr.size() >= 4) {
        auto [l, r] = get();
        // 删除前 获得输出的答案
        int ql = query(*l);
        if (ql == lst) return *l;
        int qr = query(*r);
        if (qr == ql) return *r;
        if (qr == lst) {
            // 若不变 删除两端
            erase(tr.begin(), next(l));
            erase(r, tr.end());
        } else {
            erase(l, next(r));
        }
        lst = qr;
    }
    for (auto it = tr.begin(); it != tr.end();) {
        int r = query(*it);
        if (r == lst) return *it;
        lst = r;
        tr.erase(it++);
    }
    return -1;
}
int main() {
    int res = solve();
    cout << "! " << res << endl;
    return 0;
}