#include <bits/stdc++.h>
#define int long long

using namespace std;

signed main()
{
    int n;
    cin >> n;
    int st = 1, dr = n;
    while (st < dr)
    {
        int mij = (st + dr) /2 ;
        cout << "? " << mij << '\n';
        int t;
        cin >> t;
        if (t == 0)
            st = mij + 1;
        else
            dr = mij;
    }
    cout << "! " << st;
}