#include <bits/stdc++.h>
using namespace std;
void solve()
{
    int n;
    cin >> n;
    int rec = 0;
    auto q = [&](int x) -> int
    {
        cout << "? " << x << endl;
        int res;
        cin >> res;
        return res;
    };
    int l = 1, r = n, pre = 0;
    while (l < r)
    {
        int mid = (l + r + 1) >> 1;
        int rec = q(l);
        if (pre == rec)
        {
            cout << "! " << l << endl;
            return;
        }
        int res = q(mid);
        if (res == rec)
        {
            cout << "! " << mid << endl;
            return;
        }

        if (res == pre)
        {
            l = l + 1, r = mid - 1;
        }
        else
        {
            l = mid + 1;
        }
        pre = res;
        // cout << l << " " << r << endl;
    }
    cout << "! " << l << endl;
}
int main()
{
    // #ifdef x3ea
    //     freopen("in.txt", "r", stdin);
    //     freopen("out.txt", "w", stdout);
    // #endif
    //     ios::sync_with_stdio(false);
    //     cin.tie(0), cout.tie(0);
    int _ = 1;
    // cin >> _;
    while (_--)
        solve();
    return 0;
}