#include <bits/stdc++.h>
using namespace std;
#define fastio ios::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define ll long long
#define pii pair<int, int>
#define pll pair<ll, ll>
#define pb push_back
#define fi first
#define se second
ll n, l, r, mid, temp, x, c;
bool whySoUseless, ans;
int main() {
fastio;
cin >> n;
l = 1;
r = n;
temp = 1;
while (l < r) {
temp = -temp;
l = (l+r-1)/2;
c += temp*l;
x = max(x, 1 - c);
l++;
}
cout << "? " << x << endl;
cin >> whySoUseless;
l = 1;
r = n;
temp = 1;
while (l < r) {
temp = -temp;
mid = (l+r-1)/2;
x += temp*mid;
cout << "? " << x << endl;
cin >> ans;
if (ans) {
r = mid;
} else {
l = mid + 1;
}
}
cout << "= " << l << endl;
}
