#include <bits/stdc++.h>
using namespace std;
#define int long long
#define f first
#define s second
#define pii pair<int,int>
#define pb push_back
#define eb emplace_back
#define _ mxn
int n, m, a, b, t, ans=1;
deque<int> v;
bool check(int l, int r){
cout<<"? "<<l<<' '<<r<<'\n'<<flush;
bool w; cin>>w;
return w;
}
signed main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin>>n;
int l=1, r=2;
while(r<=n){
while(!check(l, r)&&l<=r){
l++;
}
if(check(l, r)){
ans=max(ans, r-l+1);
}
r++; l--;
}
cout<<ans;
}
