#include <bits/stdc++.h>
using namespace std;
int32_t main() {
ios::sync_with_stdio(0);
cin.tie(0);
int n; cin >> n;
map<pair<int, int>, bool> mp;
auto query=[&](int l, int r) {
auto it=mp.find({l, r});
if (it!=mp.end()) return it->second;
cout << "? " << l << " " << r << endl;
cout.flush();
int res;
if (!(cin >> res)) exit(0);
return mp[{l, r}]=(res==1);
};
auto ans=[&](int answer) {
cout << "! " << answer << endl;
cout.flush();
exit(0);
};
int best=1;
{
int l=1;
for (int r=3; r<=n; r++) {
if (l==0) l++;
else if (query(l, r)) {
best=max(best, r-l+1);
l--;
} else l++;
}
}
{
int l=1;
for (int r=2; r<=n; r++) {
if (l==0) l++;
else if (query(l, r)) {
best=max(best, r-l+1);
l--;
} else l++;
}
}
ans(best);
}
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