#include <bits/stdc++.h>
using namespace std;
#define int long long
int32_t main() {
ios::sync_with_stdio(0);
cin.tie(0);
int n; cin >> n;
auto query=[&](int l, int r) {
cout << "? " << l << " " << r << endl;
cout.flush();
int res; cin >> res;
return res==1;
};
auto ans=[&](int answer) {
cout << "! " << answer << endl;
cout.flush();
exit(0);
};
vector<int> c1(n+1, 0), c2(n+1, 0);
{
int l=1, r=0;
for (int i=1; i<=n; i++) {
int k=1;
if (i<=r) k=min(c1[l+r-i], r-i+1);
while (i-k>=1 && i+k<=n) {
if (!query(i-k, i+k)) break;
k++;
}
c1[i]=k;
if (i+k-1>r) {
l=i-k+1;
r=i+k-1;
}
}
}
{
int l=1, r=0;
for (int i=1; i<=n; i++) {
int k=0;
if (i<=r) k=min(c2[l+r-i+1], r-i+1);
while (i-k>=1 && i+k+1<=n) {
if (!query(i-k, i+k+1)) break;
k++;
}
c2[i]=k;
if (i+k>r) {
l=i-k+1;
r=i+k;
}
}
}
int best=0;
for (int i=1; i<=n; i++) {
best=max(best, c1[i]*2-1);
best=max(best, c2[i]*2);
}
ans(best);
}
