#include "bits/extc++.h"
using namespace std;
template <typename T>
void dbgh(const T& t) {
cerr << t << endl;
}
template <typename T, typename... U>
void dbgh(const T& t, const U&... u) {
cerr << t << " | ";
dbgh(u...);
}
#ifdef DEBUG
#define dbg(...) \
cerr << "L" << __LINE__ << " [" << #__VA_ARGS__ << "]" \
<< ": "; \
dbgh(__VA_ARGS__)
#else
#define cerr \
if (false) \
cerr
#define dbg(...)
#endif
#define endl "\n"
#define long int64_t
#define sz(x) int((x).size())
namespace s1 {
void solve(int n) {
vector<int> vals;
for (int i = 1; i <= n; i += 32) {
vals.push_back(i);
}
vector<int> ord;
int l = 0, r = sz(vals);
while (l < r) {
ord.push_back(vals[l++]);
if (l < r) {
ord.push_back(vals[--r]);
}
}
reverse(begin(ord), end(ord));
for (auto& a : ord) {
cout << "? " << a << endl;
}
int _;
cin >> _;
int up = 0;
for (int i = 0; i < sz(ord) - 1; i++) {
int x;
cin >> x;
if (!x) {
up = abs(ord[i + 1] - ord[i]);
}
}
int prev = 1;
bool b = true;
for (int i = min(n - 1, up + 31); i > up; i--) {
if (b) {
prev += i;
} else {
prev -= i;
}
b ^= true;
cout << "? " << prev << endl;
int x;
cin >> x;
if (!x) {
cout << "= " << i + 1 << endl;
return;
}
}
cout << "= " << up + 1 << endl;
}
}
long n;
set<long> vis;
bool valid(long x) {
return 1 <= x && x <= n && !vis.count(x);
}
long mmid() {
long lg = __lg(n);
if ((1 << lg) == n) {
return (1 + n) / 2;
}
return n - (1 << lg);
}
long dfs(long l, long r) {
if (l == r) {
return 1;
}
long mid = (l + r) / 2;
long x = dfs(mid + 1, r);
if (valid(x - mid)) {
return x - mid;
} else {
return x + mid;
}
}
long query(long x) {
dbg(x);
assert(valid(x));
vis.insert(x);
cout << "? " << x << endl;
cin >> x;
return x;
}
bool check(long l, long r, long prev, long val) {
if (l == r) {
return true;
}
long mid = (l + r) / 2;
long nxt = prev + mid;
if (!valid(nxt)) {
nxt = prev - mid;
if (!valid(nxt)) {
return false;
}
}
vis.insert(nxt);
bool ans;
if (val <= abs(nxt - prev)) {
ans = check(l, mid, nxt, val);
} else {
ans = check(mid + 1, r, nxt, val);
}
vis.erase(nxt);
return ans;
}
bool check(long start) {
static mt19937 cowng(chrono::steady_clock::now().time_since_epoch().count());
vis.clear();
vis.insert(start);
for (int i = 0; i < 10000; i++) {
long x = cowng() % n + 1;
if (!check(1, n, start, x)) {
return false;
}
}
return true;
}
void solve(long l, long r, long prev) {
if (l == r) {
cout << "= " << l << endl;
return;
}
long mid = (l + r) / 2;
long nxt = prev + mid;
if (!valid(nxt)) {
nxt = prev - mid;
}
if (query(nxt)) {
solve(l, mid, nxt);
} else {
solve(mid + 1, r, nxt);
}
}
void solve() {
cin >> n;
if (n <= 1000) {
s1::solve(n);
return;
}
long start = dfs(1, n);
for (long i = max(long(1), start - 100); i <= min(n, start + 100); i++) {
if (check(i)) {
dbg(i);
vis.clear();
query(start);
solve(1, n, start);
return;
}
}
assert(false);
}
int main() {
ios_base::sync_with_stdio(false);
cin.exceptions(ios::failbit);
solve();
}
