// File colors.cpp created on 16.10.2025 at 16:20:19
#include <bits/stdc++.h>
using i64 = long long;
#ifdef DEBUG
#include "/home/ahmetalp/Desktop/Workplace/debug.h"
#else
#define debug(...) void(23)
#endif
i64 N;
#ifdef LOCAL
i64 C;
i64 lst = -1;
#endif
bool ask(i64 x) {
assert(1 <= x && x <= N);
bool res;
std::cout << "? " << x << std::endl;
#ifdef LOCAL
if (lst == -1) {
res = 0;
} else {
res = std::abs(x - lst) >= C;
}
lst = x;
#else
std::cin >> res;
#endif
return res;
}
i64 find_start() {
std::vector<i64> jmp;
i64 x = 1;
while (x < N) {
i64 nx = x + (N - x + 1) / 2 - 1;
jmp.emplace_back(nx);
x = nx + 1;
}
std::reverse(jmp.begin(), jmp.end());
i64 p = N, dir = -1;
for (auto i : jmp) {
p += i * dir;
dir *= -1;
}
if (dir == +1) {
return p;
} else {
return N - p + 1;
}
}
int main() {
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
std::cin >> N;
#ifdef LOCAL
std::cin >> C;
#endif
i64 p = find_start();
debug(p);
ask(p);
i64 len = N, dir = +1, ans = 0;
while (len > 1) {
i64 m = len / 2;
i64 np = p + dir * (ans + m);
debug(np);
bool res = ask(np);
if (res == 1) {
len = m;
} else {
ans += m;
len -= m;
}
dir *= -1;
p = np;
}
ans += 1;
std::cout << "= " << ans << std::endl;
#ifdef LOCAL
assert(ans == C);
#endif
return 0;
}
