#include<bits/stdc++.h>
using namespace std;
#include<atcoder/all>
using namespace atcoder;
using ll = long long;
int n;

void solve(){
	vector<int> a;
	for(int i = 0;i<n/2;i++){
		cout<<"? "<<i*2<<' '<<i*2+1<<'\n'<<flush;
		int x;
		cin >> x;
		if(x==i*2){
			cout<<"! "<<i*2+1<<'\n'<<flush;
			return;
		}
		if(x==i*2+1){
			cout<<"! "<<i*2<<'\n'<<flush;
			return;
		}
	}
	cout<<"! "<<n-1<<'\n'<<flush;
}

signed main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	cin >> n;
	solve();
}