#include <iostream>

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