#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=1e5+10;
int n,m,k,q,ans;
int ask(int x){
	cout<<"? "<<x<<endl;
	//cout.flush();
	int res;
	cin>>res;
	return res;
}
void solve(){
	cin>>n;
	k=0;
	for(int i=1;i<=1;i++){
		int kk=ask(i);
		if(k==kk){
			cout<<"! "<<i<<endl;
			return;
		}
		k=kk;
	}
	k=1;
	int l=2,r=n;
	while(l<=r){
		int mid=(l+r)/2;
		ans=ask(mid);
		if(ans==k){
			cout<<"! "<<mid<<endl;
			return;
		}
		if(k<ans){
			l=mid+1;
		}
		else{
			r=mid-1;
		}
		k=ans;
	}
	
}
signed main(){
	int T=1;
	//cin>>T;
	while(T--){
		solve();
	}
}