// Created by qyy on 2024/4/6.

#include <bits/stdc++.h>

using namespace std;

#define int long long

const int inf = 0x3f3f3f3f3f3f3f3f;
const int N = 2e5 + 10;
const int mod = 1e9 + 7;
int lastans, n, a[N];

void solve() {
    cin >> n;
    lastans = 0;
    int newans = 0;
    int l = 1, r = n;
    while(l <= r){
        int mid = (l + r) >> 1;
        cout << "? " << mid << endl;
        cin >> newans;
        if(newans == lastans){
            cout << "! " <<  mid << endl;
            return ;
        }else if(newans > lastans){
            l = mid + 1;
            lastans = newans;
        }else{
            r = mid - 1;
            lastans = newans;
        }
    }
}

signed main() {
//    ios::sync_with_stdio(false);
//    cin.tie(0);
    int t = 1;
    //cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}