#include <bits/stdc++.h>
#define fr(i, a, b) for (int i = (a); i <= (b); ++i)
#define rf(i, a, b) for (int i = (a); i >= (b); --i)
#define fe(x, y) for (auto& x : y)
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
#define pw(x) (1LL << (x))
using namespace std;
mt19937_64 rng(228);
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
template <typename T>
using oset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#define fbo find_by_order
#define ook order_of_key
template <typename T>
bool umx(T& a, T b) {
return a < b ? a = b, 1 : 0;
}
template <typename T>
bool umn(T& a, T b) {
return a > b ? a = b, 1 : 0;
}
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
template <typename T>
using ve = vector<T>;
#ifdef LOCAL
const bool DEBUG = 1;
#else
const bool DEBUG = 0;
#endif
ll n, C;
set<ll> used;
ll last;
bool ask(ll x) {
assert(!used.count(x));
used.insert(x);
cout << "? " << x << "\n" << flush;
if (DEBUG) {
if (abs(x - last) >= C) {
last = x;
return 1;
} else {
last = x;
return 0;
}
}
last = x;
int val;
cin >> val;
return val;
}
int main() {
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#else
// ios::sync_with_stdio(0);
// cin.tie(0);
#endif
cin >> n;
if (DEBUG) {
cin >> C;
}
ask(1);
bool who = 0;
rf (now, n - 1, 1) {
if (who == 0) {
if (!ask(last + now)) {
cout << "= " << now + 1 << "\n";
return 0;
}
} else {
if (!ask(last - now)) {
cout << "= " << now + 1 << "\n";
return 0;
}
}
who ^= 1;
}
cout << "= " << 1 << "\n";
return 0;
}
