#include <bits/stdc++.h>
using ll=long long;
#define S second
#define F first
#define endl '\n'
#define spid ios_base::sync_with_stdio(false);cin.tie(NULL);
const int mod=1e9+7;
const double pi=3.14159265359;
const int maxn=200001;
using namespace std;

int n;

int main(){
	cin>>n;
	int l=1,r=n;
	int mid,last=0;
	while(l<r){
		mid=(l+r)/2;
		cout<<"? "<<mid<<endl;
		int x;
		cin>>x;
		if(x){
			r=mid;
		}
		else l=mid+1;
	}
	cout<<"! "<<l<<endl;
}