#include <bits/stdc++.h>
using namespace std;
 
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pi;
#define pb push_back
#define mp make_pair
#define f first
#define s second

int ask(int x){
    cout << "? " << x << '\n' << flush;
    int ans;
    cin >> ans;
    return ans;
}

void solve(){
    int n;
    cin >> n;
    int l = 1, r = n;
    while(l < r){
        int mid = (l+r)/2;
        int ans = ask(mid);
        if(ans == 0)
            l = mid+1;
        else
            r = mid;
    }   
    cout << "! " << l << '\n';
}  
 
int main(){
    //freopen("darb.in", "r", stdin);
    //freopen("darb.out", "w", stdout);
    ios::sync_with_stdio(0); cin.tie(0);
    int t = 1;
    //cin >> t;
    while(t--){
        solve();
    }
}