#include <bits/stdc++.h>
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define ar array
using namespace std;
typedef long long ll;
typedef pair<int, int> ii;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int maxn = 2e5 + 5, mod = 1e9 + 7;
int go(ll x)
{
cout << "? " << x << endl;
int v; cin >> v;
return v;
}
void solve(void)
{
ll n; cin >> n;
vector<ll> path;
ll lo = 1, hi = n - 1;
while(lo <= hi){
ll mid = (lo + hi) / 2;
path.pb(mid);
if(lo == hi && mid == n - 1) break;
lo = mid + 1;
}
ll st = n; int go_left = 1;
reverse(path.begin(), path.end());
for(auto i : path){
if(go_left) st -= i;
else st += i;
go_left ^= 1;
}
go(st);
lo = 1, hi = n - 1;
while(lo <= hi){
ll mid = (lo + hi) / 2;
if(go_left) st -= mid;
else st += mid;
if(go(st)) hi = mid - 1;
else lo = mid + 1;
go_left ^= 1;
}
cout << "= " << lo << endl;
}
signed main(void)
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
/*#ifdef LOCAL
freopen("A.INP", "r", stdin);
freopen("A.OUT", "w", stdout);
#endif // LOCAL*/
int tc; tc = 1;
while(tc--){
solve();
}
}
