#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())
// 0 = x > query
// 1 = x <= query
long n;
long search(long l, long r, bool add) {
if (l == r) {
if (add) {
return 1;
} else {
return n;
}
}
long mid = (l + r - 1) / 2;
long nxt = search(mid + 1, r, !add);
if (add) {
return nxt - mid;
} else {
return nxt + mid;
}
}
void solve(long l, long r, long prev, bool add) {
static set<long> vis;
if (l == r) {
cout << "= " << l << endl;
return;
}
long mid = (l + r - 1) / 2;
if (add) {
prev += mid;
} else {
prev -= mid;
}
assert(vis.insert(prev).second);
cout << "? " << prev << endl;
int ans;
cin >> ans;
if (ans) {
solve(l, mid, prev, !add);
} else {
solve(mid + 1, r, prev, !add);
}
}
void solve() {
cin >> n;
long start = search(1, n, true);
dbg(start);
cout << "? " << start << endl;
int _;
cin >> _;
solve(1, n, start, true);
}
int main() {
ios_base::sync_with_stdio(false);
cin.exceptions(ios::failbit);
solve();
}
