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

int n;
int main(){
    cin >> n;
    int l = 1, r = n;
    int ans = 0;
    while(l <= r){
        int tm = (l + r) / 2;
        cout << "? " << tm << '\n';
        cout.flush();
        int nr;
        cin >> nr;
        if(nr){
            ans = max(ans, tm);
            r = tm - 1;
        }else{
            l = tm + 1;
        }
    }
    cout << "! " << ans << '\n';
    cout.flush();
}