#include <iostream>
#include <algorithm>
#include <vector>
#include <deque>
#include <queue>
#include <set>
#include <map>
#include <limits>
#include <cmath>
#include <iomanip>
#include <functional>
#include <random>
#include <set>
#include <atcoder/string>
#include <unordered_map>
#include <climits>
#include <atcoder/lazysegtree>

using namespace std;
using ll = long long;
using namespace atcoder;

int solve()
{
    ll N;
    cin >> N;
    if (N % 2 == 1){
        for(int i = 0;i < N;i+= 2){
            cout << "? " << i << " " << i+1 << endl;
            ll ret;
            cin >> ret;
            if (ret == i || ret == i+1){
                cout << "? " << i << " " << N-1 << endl;
                ll ret2;
                cin >> ret2;
                if (ret2 == N-1){
                    cout << i << endl;
                }else{
                    cout << i+1 << endl;
                }
                return 0;
            }
        }
        cout << N-1 << endl;
    }else{
        for(int i = 0;i+2< N;i+= 2){
            cout << "? " << i << " " << i+1 << endl;
            ll ret;
            cin >> ret;
            if (ret == i || ret == i+1){
                cout << "? " << i << " " << N-1 << endl;
                ll ret2;
                cin >> ret2;
                if (ret2 == N-1){
                    cout << i << endl;
                }else{
                    cout << i+1 << endl;
                }
                return 0;
            }
        }
        cout << "? " << 0 << " " << N-1 << endl;
        ll ret3;
        cin >> ret3;
        if (ret3 == 0){
            cout << N-1 << endl;
        }else{
            cout << N-2 << endl;
        }
    }
    return 0;
}
int main()
{
    // ll T;
    // cin >> T;
    // while (T--)
    // {
        solve();
    // }
    cout << flush;
    return 0;
}