#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
typedef long long ll;
typedef pair<ll, ll> ii;
typedef vector<ll> vi;
ll comp(ll N) {
ll low = 1;
ll high = N - 1;
ll curr = 0;
ll dir = 1; // 1 means next is going up, -1 means down
vi all;
all.pb(0);
// found that C = N always gives the extreme case
while (low <= high) { // false, false, false, true, true, true
ll mid = (low + high) / 2;
curr += mid * dir;
dir = -dir;
all.pb(curr);
if (mid >= N)
high = mid - 1;
else
low = mid + 1;
}
ll currmin = 2e18;
ll currmax = -2e18;
for (ll i : all) {
currmin = min(currmin, i);
currmax = max(currmax, i);
}
return (-currmin + 1); // starting point
}
ll query(ll x) {
cout<<"? "<<x<<endl;
cout.flush();
ll val;
cin>>val;
return val;
}
int main() {
ll N;
cin>>N;
ll base = comp(N); // start here so we never go outside [1, N]
// solve
ll low = 1;
ll high = N - 1;
ll ans = N; // value of C
ll curr = base;
query(curr);
ll dir = 1; // 1 means next is going up, -1 means down
vi all;
all.pb(0);
while (low <= high) { // false, false, false, true, true, true
ll mid = (low + high) / 2;
curr += mid * dir;
dir = -dir;
all.pb(curr);
if (query(curr)) {
high = mid - 1;
ans = mid;
}
else {
low = mid + 1;
}
}
cout<<"= "<<ans<<endl;
}
