#include<iostream>
using namespace std;
int N;
int main()
{
	cin>>N;
	for(int i=0;i+1<N;i+=2)
	{
		cout<<"? "<<i<<" "<<i+1<<endl;
		int k;cin>>k;
		if(k==i||k==i+1)
		{
			cout<<"! "<<i+i+1-k<<endl;
			return 0;
		}
	}
	cout<<"! "<<N-1<<endl;
}