#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
using ll = long long;
using ld = long double;
using ii = pair<int, int>;
using pll = pair<ll, ll>;
using uid = uniform_int_distribution<int>;
using ordered_set = tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>;
using ordered_multiset = tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update>;
const int inf = int(1e9) + 7;
const ll INF = ll(1e18) + 7;
#define X first
#define Y second
//~ mt19937 rng(chrono::steady_clock().now().time_since_epoch().count());
//~ int rand(int a, int b) {
//~ return uid(a, b)(rng);
//~ }
void boost() {
ios_base::sync_with_stdio(0);
cin.tie(0);
}
ll n;
ll act;
bool ask(ll x) {
if(x > n) {
ask(act - (x - n));
x = n;
}
if(x < 1) {
ask(act + (1 - x));
x = 1;
}
act = x;
cout << "? " << x << endl;
//~ fflush(stdout);
int xx;
cin >> xx;
return (xx == 1);
}
void solve() {
cin >> n;
ll first = 1;
ll m = 0, pocz = 1, mid;
while(pocz < n) {
mid = (pocz + n) / 2;
if(m)
first += (mid - pocz + 1);
m ^= 1;
pocz = mid + 1;
}
ask(first);
int dir = 1;
pocz = 1;
ll kon = n;
while(pocz < kon) {
mid = (pocz + kon) / 2;
if(ask(act + ll(dir) * mid))
kon = mid;
else
pocz = mid + 1;
dir = -dir;
}
cout << "= " << pocz << endl;
//~ fflush(stdout);
}
int main() {
//~ boost();
int t = 1;
//~ cin >> t;
while(t--) {
solve();
}
return 0;
}
