#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<int, int> PII;
typedef pair<double, double> PDD;
typedef unsigned long long ull;
int n,val;
int main() {
    cin>>n;
    int left = 1 , right = n;
    cout << "? 1\n";
    cout.flush();
    int t;
    cin >> t;
    if (!t) {
        cout << "! 1\n";
        cout.flush();
        return 0;
    }
    val = t;
    left = 2;
    while(left < right){
        int mid = (left + right) >> 1;
        cout<<("? ")<<mid<<"\n";
        cout.flush();
       // s.insert(mid);
       //int t;
        cin>>t;
        if(t > val){
            left = mid + 1;
        }else if(t < val){
            right = mid - 1;
        }else if(t == val){
            cout<<"! "<<mid<<'\n';
            cout.flush();
            return 0;
        }
        val = t;

    }
    cout<<"! "<<left<<'\n';
    cout.flush();
    return 0;

    //return 0;
}