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

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int N, v;
    cin >> N;
    for(int i = 0; i < N; i += 2){
        cout << "? " << i << " " << i + 1 << endl;
        cin >> v;
        if(v == i || v == i + 1){
            cout << "! " << ((i + 1) ^ i ^ v) << endl;
            return 0;
        }
    }
    cout << "! " << N - 1 << endl;
}