#include <iostream>
#define int long long

using namespace std;
int n,k,st,dr,mij,sol;
bool a;
signed main()
{
    cin>>n;
    st=1;dr=n;
    while(st<=dr){
       mij=(st+dr)/2;
       cout<<"? "<<mij;
       cin>>a;
       cout.flush();
       if(a){
            sol=mij;
            dr=mij-1;
       }
       else{
            st=mij+1;
       }

    }
    cout<<"! "<<sol;

}