// 提出時にassertはオフ
#ifndef DEBUG
#ifndef NDEBUG
#define NDEBUG
#endif
#endif

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

#define ALL(x) (x).begin(), (x).end()
template <class T> using vec = vector<T>;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int N;
    cin >> N;
    for(int i = 0; i < N - 1; i += 2) {
        cout << "? " << i << " " << i + 1 << endl;
        int ans;
        cin >> ans;
        if(ans == i) {
            cout << "! " << i + 1 << endl;
            return 0;
        }
        if(ans == i + 1) {
            cout << "! " << i << endl;
            return 0;
        }
    }
    cout << "! " << N - 1 << endl;
}