#include <bits/stdc++.h>
using namespace std;

int n,st,dr,m,x;

int main()
{
    cin >> n;
    st=1;
    dr=n;
    while(st<dr){
        m=(st+dr)/2;
        cout << "? " << m << endl;
        cin >> x;
        if(x==0){
            st=m+1;
        }
        else dr=m;
    }
    cout << "! " << st;
    return 0;
}