// By AmmarDab3an

#include "bits/stdc++.h"

using namespace std;

#define int int64_t
#define ll  int64_t

// typedef unsigned int        uint;
// typedef long long int       ll;
// typedef unsigned long long  ull;
typedef pair<int, int>    pii;
typedef pair<ll, ll>      pll;
typedef pair<int, pii>    iii;
typedef pair<ll, pll>     lll;
typedef vector<int>       vi;
typedef vector<ll>        vl;
typedef vector<pii>       vpii;
typedef vector<pll>       vpll;

#define endl '\n'
#define fastIO ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define freopenI freopen("input.txt", "r", stdin);
#define freopenO freopen("output.txt", "w", stdout);

const int INF = 0x3f3f3f3f;
const ll INFLL = 0x3f3f3f3f3f3f3f3f;
const int MOD = 1e9 + 7;
const double EPS = 1e-9;
const double  PI = acos(-1);

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

int rand(int x, int y) {
	return uniform_int_distribution<int>(x, y)(rng);
}

int mul(int a, int b){
	int ret = (1ll * (a%MOD) * (b%MOD)) % MOD;
	return (ret+MOD)%MOD;
}

int add(int a, int b){
	int ret = (1ll * (a%MOD) + (b%MOD)) % MOD;
	return (ret+MOD)%MOD;
}

int pow_exp(int n, int p){
	if(!p) return 1;
	if(p&1) return mul(n, pow_exp(n, p-1));
	int tmp = pow_exp(n, p/2);
	return mul(tmp, tmp);
}

int inv(int x){
	return pow_exp(x, MOD-2);
}

const int  MAX = 2e5 + 10;
const int NMAX = 2e5 + 10;
const int MMAX = 2e5 + 10;
const int LOG_MAX = ceil(log2(double(NMAX)));
const int BLOCK = ceil(sqrt(double(NMAX)));

int fac[NMAX], ifac[NMAX];

void init(){

	fac[0] = 1;
	for(int i = 1; i < NMAX; i++){
		fac[i] = mul(fac[i-1], i);
	}

	ifac[NMAX-1] = inv(fac[NMAX-1]);
	for(int i = NMAX-2; i >= 0; i--){
		ifac[i] = mul(ifac[i+1], i+1);
	}
}

int choose(int n, int c){
	assert(n >= c);
	return mul(fac[n], mul(ifac[c], ifac[n-c]));
}

int cnt = 0;
int ask(int x){

	assert(++cnt <= 40);

	cout << "? " << x << endl << flush;
	int ret;
	cin >> ret;
	return ret;
}

int ans(int x){
	cout << "! " << x << endl << flush;
	exit(0);
}

int32_t main(){

	int n;
	cin >> n;

	int l = 1;
	int r = n;

	int lst = 0;

	while(l < r){

		int mid = (l+r)/2;

		int a0 = ask(mid);

		if(lst==a0){
			ans(mid);
		}
		else{
			lst = a0;
		}

		int a1 = ask(l);

		if(lst==a1){
			ans(l);
		}
		else{

			if(a1 > a0){
				l = mid+1;
			}
			else{
				r = mid-1;
			}

			lst = a1;
		}
	}

	assert(false);
}