#include <bits/stdc++.h>

using namespace std;

int main()
{
    int n;
    cin.tie(0); cin.sync_with_stdio(false);
    cin>>n;
    int st=1, dr=n, mid=-1, ans=-1, poz=-1;
    while (st<=dr) {
        mid=(st+dr)/2;
        cout<<"? "<<mid; cout.flush();
        cin>>ans;
        if (ans==0) { //K>x
            st=mid+1;
        }
        else { //K<=X
            poz=mid;
            dr=mid-1;
        }
    }
    cout<<"! "<<poz;
    return 0;
}