#include <bits/stdc++.h>
using namespace std;

#define x first
#define y second
typedef pair<int, int> PII;
typedef long long ll;

vector<int> Q{0};

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

void anser(int x)
{
    cout << "! " << x << endl;
}

int work(int l, int r)
{
    if(r - l + 1 == 1) return l;
    else if(r - l + 1 == 2)
    {
        int res = ask(l);
        if(res == Q.back()) return l;
        else return r;
    }
    int mid = l + r >> 1;
    int res = ask(l);
    if(res == Q.back()) return l;
    Q.push_back(res);
    res = ask(mid);
    if(res == Q.back()) return mid;
    Q.push_back(res);
    if(res == Q[Q.size() - 3]) return work(l + 1, mid - 1);
    else return work(mid + 1, r);
}

void solve()
{
    int n;
    cin >> n;
    int ans = work(1, n);
    anser(ans);
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    // int T; cin >> T; while(T--)
    solve();
    return 0;
}