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

int main(){
    int n; cin >> n;
    int ans = n-1;
    for (int i = 0; i < n/2; i++){
        cout << "? " << 2*i << " " << 2*i+1 << endl;
        int k; cin >> k;
        if (k == 2*i) ans = 2*i+1;
        if (k == 2*i+1) ans = 2*i;
    }
    cout << "! " << ans << endl;
}