/**
 * Author: Andu Scheusan (not_andu)
 * Created: 17.12.2023 16:44:29
*/

#include <bits/stdc++.h>
#pragma GCC optimize("O3")

using namespace std;

typedef long long ll;

void solve(){

    int n; cin >> n;
    int left = 1, right = n, ans;
    bool ok;

    while(left <= right){
        int middle = (left + right) / 2;
        cout << "?" << middle << '\n';
        cin >> ok;
        if(ok){
            ans = middle;
            right = middle - 1;
        }
        else{
            left = middle + 1;
        }
    }

    cout << "! " << ans << '\n';

}

int main(){
    
    ios_base::sync_with_stdio(false);

    cin.tie(nullptr);
    cout.tie(nullptr);

    solve();

    return 0;
}