#include <bitset>
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#include <immintrin.h>
using namespace std;
typedef long long ll;
#define int ll
const int inf = int(1e18);
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> p2;
#define rep(i, high) for (int i = 0; i < (high); i++)
#define repp(i, low, high) for (int i = (low); i < (high); i++)
#define repe(i, container) for (auto& i : container)
#define sz(container) ((int)container.size())
#define all(x) begin(x),end(x)
inline void fast() { cin.tie(0)->sync_with_stdio(0); }
#if _LOCAL
#define assert(x) if (!(x)) __debugbreak()
#endif
int n;
int ask(int x)
{
cout << "? " << x << endl;
int resp;
cin >> resp;
return resp;
}
signed main()
{
fast();
// find starting guess.
// we will start at some number, then alternate left/right. find extreme deviation from start and place start
// based on that
vi nums;
{
int lo = 0;
int hi = n;
while (lo + 1 < hi)
{
int mid = (lo + hi) / 2;
nums.push_back(mid);
lo = mid;
}
}
int mi = n;
int pref = 0;
rep(i, sz(nums)) pref += (i % 2 ? 1 : -1) * nums[i], mi = min(mi, pref);
int start = -mi + 1;
ask(start);
// start guessing
int last = start;
int lo = 0;
int hi = n;
int i = 0;
int direction = -1;
while (lo + 1 < hi)
{
int mid = (lo + hi) / 2;
int g;
if (i % 2) g = last + mid;
else g = last - mid;
if (ask(g))
{
hi = mid;
}
else lo = mid;
last = g;
i++;
}
cout << "= " << hi << endl;
return 0;
}
