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