#include<bits/stdc++.h>
using namespace std;
//#define int long long
int query(int x){
	cout<<"? "<<x<<endl;
	cout.flush();
	int num;
	cin>>num;
	return num;
}
void solve(){
	int n;cin>>n;
	int cnt = query(1);
	if(cnt==0){
		cout<<"! "<<1<<"\n";
		return ;
	}
	int l = 1,r=n;
	while(l<r){
		int mid=(l+r+1)/2;
		if(query(mid)>=cnt) l =mid;
		else r=mid-1;
		
	}
	cout<<"! "<<l<<"\n";
}
signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0);cout.tie(0);
	int t=1;
	//cin>>t;
	while(t--){
		solve();
	}
}