#include <bits/stdc++.h>
using namespace std;
long long i, j, l, r, mid, p, q, k, t, n, m, a, b, c, d, ans, cnt, res;
const long long mod = 999993143, mod2 = 999993469;
string s;
bool check;
long double cur;
map <long long, long long> mp;
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
cin >> n;
if (n > 64){
l = 1;
r = n;
a = 1;
b = n;
res = n / 3;
mp[res] = 1;
cout << "? " << res << endl;
cin >> d;
cnt = 0;
t = res;
while (l < r){
mid = (l + r) / 2;
if (cnt % 2 == 0){
res += mid;
}
else{
res -= mid;
}
if (mp[res] == 1 || res <= 0 || res > n){
res += 1;
if (mp[res] == 1 || res <= 0 || res > n){
res -= 2;
if (mp[res] == 1 || res <= 0 || res > n){
res += 3;
if (mp[res] == 1 || res <= 0 || res > n){
res -= 4;
if (mp[res] == 1 || res <= 0 || res > n){
res += 5;
if (mp[res] == 1 || res <= 0 || res > n){
res -= 6;
if (mp[res] == 1 || res <= 0 || res > n){
break;
}
}
}
}
}
}
}
mp[res] = 1;
cout << "? " << res << endl;
cin >> d;
if (d == 0){
a = max(a, abs(t - res) + 1);
l = a;
}
else{
b = min(b, abs(t - res));
r = b;
}
c = a;
d = b;
a = min(c, d);
b = max(c, d);
cnt += 1;
t = res;
}
cout << "= " << a << endl;
}
else{
ans = 0;
l = 2;
r = n;
cout << "? 1" << endl;
cin >> d;
for (i = 2; i <= n; i += 1){
if (i % 2 == 1){
cout << "? " << l << endl;
l += 1;
}
else{
cout << "? " << r << endl;
r -= 1;
}
cin >> d;
if (d == 0){
break;
}
else{
ans += 1;
}
}
cout << "= " << n - ans << endl;
}
}
