#include <bits/stdc++.h>
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define pb push_back
#define FIO ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0)
using namespace std;
typedef long long ll;
typedef pair <ll, ll> pii;
int ask(ll x) {
cout << "? " << x << endl;
int o; cin >> o;
return o;
}
int main () {
FIO;
ll n; cin >> n;
ll cur = 0, of = 0;
for (ll i = 1, o = 0; i < n; o ^= 1) {
ll m = (n+i)/2;
cur += (-1+2*(!o))*m;
i = m+1;
of = max(of, -cur);
}
of++;
ask(of);
ll lo = 1, hi = n;
int o = 0, o1 = 0;
while (lo < hi) {
ll mid = (lo + hi) / 2;
of = of+(-1+2*(!o))*mid;
o ^= 1;
int oo = ask(of);
if (oo) hi = mid;
else lo = mid+1;
if (!o1 && oo) {
o1 = 1;
ask(mid);
o = 1; of = mid;
}
}
cout << "= " << lo << endl;
return 0;
}
