#include <bits/stdc++.h>

using namespace std;

int main()
{
    int N;
    cin >> N;
    int le = 1, ri = N; 
    int ans = 0;
    while(le <= ri) {
        int mid = (le + ri) / 2;
        cout << "? " << mid << endl;
        int t;
        cin >> t;
        if(t == 0) {
            le = mid + 1;
        }
        else if(t == 1) {
            ri = mid - 1;
            ans = mid;
        }
        else {
            return 0;
        }
    }
    cout << "! " << ans << "\n";
    return 0;
}