#include<iostream>
#include<vector>
#include<algorithm>
#include<cstring>
#include<cassert>
#include<cmath>
#include<ctime>
#include<iomanip>
#include<numeric>
#include<stack>
#include<queue>
#include<map>
#include<unordered_map>
#include<set>
#include<unordered_set>
#include<bitset>
#include<random>
using namespace std;
int N;
void solve()
{
	cin >> N;
	int cur = 0;
	while(cur*2+1 < N)
	{
		cout << "? " << 2*cur << " " << 2*cur+1 << endl;
		cout.flush();
		int z;
		cin >> z;
		if(z/2 == cur)
		{
			cout << "! " << ((2*cur)^(2*cur+1)^(z)) << endl;
			return;
		}
		cur++;
	}
	assert(N%2 == 1);
	cout << "! " << N-1 << endl;
	return;
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int T = 1;
	//cin >> T;
	while(T--) solve();
}