#include <bits/stdc++.h>

using namespace std;

int main()
{
    int N;
    cin >> N;
    int l = 1 , r = N , p;
    while (l <= r)
    {
        int m = (l + r) / 2 , nr;
        cout << "? " << m;
        cin >> nr;
        if(nr == 0)
            l = m + 1;
        else
        {
            r = m - 1;
            p = m;
        }
        cout.flush();
    }
    cout << "! " << p;
}