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

ifstream f("cbinteractiv.in");
ofstream g("cbinteractiv.out");

int n;
int st,dr,mij;
int x;

int query(int nr) {
    cout << "? " << nr << '\n';
    cin >> x;
    return x;
}

int main()
{
    cin >> n;
    st=1, dr=n;
    while (st!=dr) {
        mij = (st+dr)/2;
        if (query(mij)==1) {
            dr = mij;
        }
        else {
            st = mij+1;
        }
    }
    cout << "! " << st;
    return 0;
}