#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;
int main() {
    cin>>n;
    int left = 1 , right = n;
    int val = 0;
    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';
            return 0;
        }

    }
    cout<<"! "<<left<<'\n';
    return 0;
}