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