#include <bits/stdc++.h>

using namespace std;

int n, res, mid;

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

int main(){
    cin >> n;
    int l=1, r=n;

    while(l<=r){
        mid=(l+r)/2;

        int ans = query(mid);

        (ans == 1) ? r=mid-1 : l=mid+1;
    }

    cout << "! " << l << '\n';
    cout.flush();

    return 0;
}