#include <iostream>

using namespace std;

int n,st,dr,mij,sol,rasp;
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);

    cin>>n;
    st=1; dr=n;
    while (st<=dr)
    {
        mij=(st+dr)>>1;

        cout<<"? "<<mij;
        cout.flush();
        cin>>rasp;

        if (rasp==1)
        {
            sol=mij;
            dr=mij-1;
        }
        else
            st=mij+1;
    }

    cout<<"! "<<sol;
    cout.flush();
    return 0;
}