#include <bits/stdc++.h>
using namespace std;
ifstream f("stirling.in");
ofstream g("stirling.out");
#define f cin
#define g cout

int32_t main()
{
    int n, st = 1, dr, p;
    cin >> dr;
    while (st <= dr)
    {
        int mid = (st + dr) / 2, ans;
        cout << "? " << mid << endl;
        cin >> ans;
        if (ans)
            p = mid, dr = mid - 1;
        else
            st = mid + 1;
    }
    cout << "! " << p;
    return 0;
}