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

int main(void) {
    int n;
    cin >> n;
    for(int i = 0; i < n - 1; i += 2) {
        cout << "? " << i << " " << i + 1 << endl;
        int res;
        cin >> res;
        if(res == i) {
            cout << "! " << i + 1 << endl;
            return 0;
        }
        if(res == i + 1) {
            cout << "! " << i << endl;
            return 0;
        }
    }
    cout << "! " << n - 1 << endl;
    return 0;
}