#include <iostream>
#include <bits/stdc++.h>
#define VMAX 1000005
#define INF 2147000000
#define double long double
using namespace std;
ifstream fin ("elmaj.in");
ofstream fout ("elmaj.out");


signed main()
{
    long long int n,m,i,j,k,t,q,nr,p,aparitii,candidat,st,dr,mij;
    cin>>n;
    st=0; dr=n;
    while(dr-st>1)
    {
        mij=(st+dr)/2;
        cout<<"? "<<mij<<'\n';
        cout.flush();
        cin>>k;
        if(k==1)
            dr=mij;
        else
            st=mij;
    }
    cout<<"! "<<dr<<'\n';


    return 0;
}