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

int main(){
    int64_t N; cin >> N;
    int64_t T = N/2;
    for(int64_t i = 0; i < T; i++){
        cout << "? " << 2*i << " " << 2*i+1 << endl;
        int64_t z; cin >> z;
        if(z == 2*i or z == 2*i+1){
            cout << "! " << (z xor (2*i) xor (2*i+1)) << endl;
            return 0;
        }
    }
    cout << "! " << N-1 << endl;
}