#include<bits/stdc++.h>
using namespace std;
#define int long long
map<pair<int,int>,int>mp;
map<pair<int,int>,int>vis;
int ask(int l,int r){
if(vis[{l,r}]){return mp[{l,r}];}
cout<<"? "<<l<<" "<<r<<endl;
int ret;
vis[{l,r}]=1;
cin>>ret;
mp[{l,r}]=ret;
return ret;
}
int n;
int ar[200005];
int par[200005];
int tar[500005];
void rebuild(){
tar[1]=ar[1];
int it=2;
for(int i=2;i<=n;i++){
tar[it]=2;
tar[it+1]=ar[i];
it+=2;
}
for(int i=1;i<=n+n-1;i++){
ar[i]=tar[i];
}
}
int ps[500005];
int tme[500005];
int mod=1e9+7;
int hsh[500005];
int hsh2[500005];
int gthsh(int l,int r){
//cout<<l<<" "<<r<<endl;
int ret=(hsh[r]-hsh[l-1]+mod)%mod;
ret=(ret*tme[200000-r])%mod;
return ret;
}
int gthsh2(int l,int r){
//cout<<l<<" "<<r<<endl;
int ret=(hsh2[r]-hsh2[l-1]+mod)%mod;
ret=(ret*tme[200000-r])%mod;
return ret;
}
int typ;
int ok(int len){
if(typ==0){
len=len*2;
}else{
len=1+len*2;
}
if(len==0){return 1;}
for(int i=1;i<=n-len+1;i++){
int v=gthsh(i,i+len-1);
int vv=gthsh2(n-(i+len-1)+1,n-i+1);
if(vv==v){
return 1;
}
}
return 0;
}
signed main(){
cin>>n;
int ans=1;
for(int i=1;i<=n;i++){
int l=1;int r=min(n-i+1,i);
while(l<r){
int mi=l+(r-l+1)/2;
int ll=i-mi+1;int rr=i+mi-1;
if(mi==1||ask(ll,rr)){
l=mi;
}else{
r=mi-1;
}
}
ans=max(ans,l*2-1);
l=0;r=min(i,n-i);
while(l<r){
int mi=l+(r-l+1)/2;
int ll=i-mi+1;int rr=i+mi;
if(mi==0||ask(ll,rr)){
l=mi;
}else{
r=mi-1;
}
}
ans=max(ans,l*2);
}
cout<<"! "<<ans<<endl;
}
