#include <stdio.h>
#include <iostream>
#include <iomanip>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <array>
#include <queue>
#include <stack>
#include <set>
#include <list>
#include <limits>
#include <unordered_map>
#include <unordered_set>
#include <bitset>

#include <math.h>
#include <climits>

#pragma warning(push)
#pragma warning(disable:26498 26450 26451 26812)
#include "atcoder/all"
#pragma warning(pop)

//#include <boost/multiprecision/cpp_int.hpp>
//using namespace boost::multiprecision;
// std::setprecision(10)

using namespace std;
using namespace atcoder;

using ll = long long;
using ull = unsigned long long;
constexpr ll mod = ll(1e9) + 7;
constexpr ll mod2 = 998244353;
using mint = modint1000000007;
//using mint = modint998244353;

const double eps = 1e-9;

#define REP(i, n) for (ll i = 0; i < (n); ++i)
#define REPI(i, init, n) for (ll i = init; i < (n); ++i)
#define REPD(i, init) for (ll i = init; i >=0; --i)
#define REPE(i, c) for (const auto& i : c)

using vl = vector<ll>;
#define VL(a, n) vector<ll> a; a.assign(n, 0);
#define VLI(a, n) vector<ll> a; a.assign(n, 0); for(auto& x : a) cin >> x;
#define VSI(a, n) vector<string> a; a.assign(n, ""); for(auto& x : a) cin >> x;

using vvl = vector<vector<ll>>;
#define VVLI(a, n, m, init) vector<vector<ll>> a(n); for(auto& x : a) x.assign(m, init);

template <class T = long long> using pql = priority_queue<T>;
template <class T = long long> using pqg = priority_queue<T, vector<T>, greater<T>>;

const char* YES = "Yes";
const char* NO = "No";
void yn(bool f) { std::cout << (f ? YES : NO) << endl; };
template<class T> void ov(const T& v) { for (auto it = v.begin(); v.end(); v++) { if (it != v.begin()) cout << " "; cout << *it; } };

const ll llhuge = 1LL << 60; //十分でかいが多少足しても溢れない数値
template<class T, class U> bool chmin(T& a, const U& b) { a = min(a, b); return b == a; }
template<class T, class U> bool chmax(T& a, const U& b) { a = max(a, b); return b == a; }
template<class T> void mysort(T& v) { std::sort(begin(v), end(v)); };
template<class T, class U> void mysort(T& v, U pr) { std::sort(begin(v), end(v), pr); };
template<class T> void myrev(T& v) { std::reverse(begin(v), end(v)); };

int main() {
	cin.tie(nullptr);
	ios::sync_with_stdio(false);

	ll n;
	cin >> n;

	REP(i, n / 2) {
		cout << "? " << i * 2 << " " << i * 2 + 1 << endl;

		ll z;
		cin >> z;

		if (z == i * 2) {
			cout << "! " << i * 2 + 1;
			return 0;
		}
		if (z == i * 2 + 1) {
			cout << "! " << i * 2;
			return 0;
		}
	}

	cout << "! " << n - 1;
	return 0;
}