#include <bits/stdc++.h>

using namespace std;

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