#include "bits/stdc++.h"
#define endl '\n'
#define f first
#define s second
#define pb push_back
#define mp make_pair
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define rep(i, a, b) for (int i = (a); i < (b); ++i)
std::mt19937 rng((int) std::chrono::steady_clock::now().time_since_epoch().count());
using namespace std;
// #define int long long
 
#define dbg_loc() cerr << __PRETTY_FUNCTION__ << " : " << __LINE__ << "\n"
template<typename A, typename B> ostream& operator<<(ostream &os, const pair<A, B> &p){ 
	return os << '(' << p.first << ", " << p.second << ')'; 
}
template<typename T_container,typename T=typename enable_if<!is_same<T_container,string>::value, typename T_container::value_type>::type> 
ostream& operator<<(ostream &os, const T_container &v){ 
	os << '{'; string sep; for (const T &x : v) os << sep << x, sep = ", "; return os << '}'; 
}
void dbg_out() { cerr << endl; }
template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T){ 
	cerr << ' ' << H; 
	dbg_out(T...); 
}
#define LOCAL
#define LOCAL
#ifdef LOCAL 
#define dbg(...) cerr<<"(" << #__VA_ARGS__<<"):" , dbg_out(__VA_ARGS__) , cerr << endl
#else
#define dbg(...)
#endif
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
ll mod = (1000000007LL);
inline ll Mod(ll a, ll b){return (a%b);}
inline ll poww(ll a, ll b){ll res = 1;while (b > 0){if(b & 1) res = (res * a)%mod;a = (a * a)%mod;b >>= 1;}return res;}
ll gcd (ll a, ll b) { while (b) { a %= b,swap(a, b);}return a;}
void read(vector<int> &w, int n){w.resize(n);for(int i = 0; i < n; i++) cin>>w[i];}
void print(vector<int> &w){for(int i =0; i < sz(w); i++){if(i == sz(w) - 1) cout<<w[i]<<"\n";else cout<<w[i]<<" ";}}
 
///CUIDADO COM MAXN
#define N 1000010 // 1E6

int n, k, v[N];
string s;

bool TESTE = false;
int POS_TESTE = 3546;

vi ligados;
int query(int x){
	cout<<"? "<<x<<endl;

	int delta;
	if(!TESTE)
		cin>>delta;

	if(TESTE){
		ligados.pb(x);
		int l = 0,r=0;
		for(auto w: ligados){
			if(w < POS_TESTE){
				l++;
			}
			if(w > POS_TESTE) r++;
		}

		return abs(l-r);
	}


	return delta;
}
int32_t main(){
	// ios::sync_with_stdio(false); cin.tie(0);
	cin>>n;
	if(n <= 20){
		int curr=-1e9;
		for(int i = 1; i <= n; i++){
			int delta = query(i);
			if(delta == curr){
				cout<<"! "<<i<<endl;
				return 0;
			}
			curr=delta;
		}
		return 0;
	}
	int curr=-1e9;

	for(int i = 1; i <= 20; i++){
		int delta = query(i);
		if(delta == curr){
			cout<<"! "<<i<<endl;
			return 0;
		}
		curr=delta;
	}

	int ini = 21, fim = n, best;
	for(int cnt = 1; cnt <= 20; cnt ++){
		int mid = (ini + fim)/2;
		int delta = query(mid);
		if(delta == curr){
			cout<<"! "<<mid<<"\n";
			return 0;
		}
		if(delta < curr){ // mid ta a direita de opt
			fim=mid-1;
		}
		else ini = mid + 1;

		curr = delta;
	}

	cout<<"! "<<best<<endl;

}