#include <iostream>
#include <cstdio>
#include <cstring>

using namespace std;

int main()
{
	int n;
	cin >> n;
	int stanga, dreapta, mijloc;
	stanga=1;
	dreapta=n;
	while(stanga<dreapta)
	{
	
		mijloc=(stanga+dreapta)/2; // 1) 5; 2) 3;
		cout <<"? "<< mijloc << endl;
		int raspuns;
		cin >> raspuns;
		if(raspuns==0)
			stanga=mijloc+1; 2) 2, ...
		else
			dreapta=mijloc; // 1) 5
	}
	cout <<"! "<< stanga;
			
}