// Success consists of going from failure to failure without loss of enthusiasm
#include <bits/stdc++.h>
using namespace std;
#define nl '\n'
template<class T> using V = vector<T>;
using vi = V<int>;
int main() {
cin.tie(0)->sync_with_stdio(0);
int N; cin >> N;
auto ask = [&](int l, int r) {
if (l < 0 || r >= N) return 0;
cout << "? " << l + 1 << " " << r + 1 << endl;
int res; cin >> res; return res;
};
int ANS = 1;
// odd
{
vi ans(N); int lo = 0, hi = 0;
for(int i = 0; i < N; i++) {
if (i > 0) {
ans[i] = min(hi - i, ans[hi - i + lo]);
ans[i] = max(0, ans[i]);
}
while(ask(i - ans[i] - 1, i + ans[i] + 1)) ++ans[i];
if (ans[i] + i > hi) lo = i - ans[i], hi = i + ans[i];
}
// for(auto& x : ans) cout << x << " ";
// cout << nl;
int bst = *max_element(begin(ans), end(ans));
ANS = max(ANS, 2 * bst + 1);
}
// even
{
vi ans(N, -1); int lo = 0, hi = 0;
for(int i = 1; i < N; i++) {
// cout << lo << " " << hi << " " << hi - i + 1 + lo << endl;
if (i > 1) ans[i] = min(hi - i + 1, ans[hi - i + 1 + lo]);
// cout << ans[i] << endl;
while(ask(i - 1 - ans[i] - 1, i + ans[i] + 1)) ++ans[i];
if (ans[i] + i > hi) lo = i - 1 - ans[i], hi = i + ans[i];
}
// for(auto& x : ans) cout << x << " ";
// cout << nl;
int bst = *max_element(begin(ans), end(ans));
ANS = max(ANS, 2 * bst + 2);
}
cout << "! " << ANS << endl;
exit(0-0);
}
