#include <bits/stdc++.h>

using namespace std;

int main()
{
    int n;

    cin >> n;
    int left = 1, right = n;
    while(left < right) {
        int mid = (left + right) >> 1;
        cout << "? " << mid << "\n";
        fflush(stdout);
        int ans;
        cin >> ans;
        if(ans == 0) {
            left = mid + 1;
        }
        else if(ans == 1) {
            right = mid;
        }
        else {
            return 0;
        }
    }
    cout << "! " << left;
    return 0;
}