#include<bits/stdc++.h>

using namespace std;
using ll = long long;

int main(){
    ll n;
    cin >> n;
    for(int i = 0;i < n;i += 2){
        int x = i;
        int y = i+1;
        if(y >= n){
            cout << '!' << ' ' << x << endl;
            return 0;
        }

        cout << "? " << x << ' ' << y << endl;
        int tmp;
        cin >> tmp;
        if(tmp == x){
            cout << "! " << y << endl;
            return 0;
        }
        else if(tmp == y){
            cout << "! " << x << endl;
            return 0;
        }
    }
}