#include<iostream>

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