#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001



int main(){
	
	int n;
	cin>>n;
	
	rep(i,n/2){
		int x = i*2;
		int y = i*2+1;
		cout<<"? "<<x<<' '<<y<<endl;
		int z;
		cin>>z;
		if(z==x){
			cout<<"! "<<y<<endl;
			return 0;
		}
		if(z==y){
			cout<<"! "<<x<<endl;
			return 0;
		}
	}
	cout<<"! "<<n-1<<endl;
		
	
	return 0;
}