#include <iostream>
using namespace std;
int n,st,dr,mid,x;
int main() {
    cin>>n;
    st=1;
    dr=n;
    while (st<=dr) {
        mid=(st+dr)/2;
        cout<<"? "<<mid<<"\n";
        cout.flush();
        cin>>x;
        if (x==0)
            st=mid+1;
        else
            dr=mid-1;
    }
    cout<<"! "<<st;
    return 0;
}