#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;
for(int i=1;i<=n-1;i++){
int v=ask(i,i+1);
if(v==1){
ar[i+1]=ar[i];
}else{
ar[i+1]=ar[i]^1;
}
}
for(int i=1;i<=n;i++){
tar[i]=ar[i];
// cout<<ar[i]<<" ";
}//cout<<endl;
reverse(tar+1,tar+n+1);
tme[0]=1;
for(int i=1;i<=200000;i++){
tme[i]=tme[i-1]*31%mod;
hsh[i]=(hsh[i-1]+(ar[i]+1)*tme[i])%mod;
hsh2[i]=(hsh2[i-1]+(tar[i]+1)*tme[i])%mod;
}/*
for(int i=1;i<=n;i++){
cout<<hsh[i]<<" ";
}cout<<endl;
for(int i=1;i<=n;i++){
cout<<hsh2[i]<<" ";
}cout<<endl;
for(int i=1;i<=n;i++){
cout<<ar[i]<<" ";
}cout<<endl;
for(int i=1;i<=n;i++){
cout<<tar[i]<<" ";
}cout<<endl;*/
int l=0;int r=n;
while(l<r){
int mi=l+(r-l+1)/2;
if(ok(mi)){
l=mi;
}else{
r=mi-1;
}
}
int ans=l*2;
l=0;r=n;
typ=1;
while(l<r){
int mi=l+(r-l+1)/2;
if(ok(mi)){
l=mi;
}else{
r=mi-1;
}
}
ans=max(l*2+1,ans);
cout<<"! "<<ans<<endl;return 0;
/*
rebuild();
int l;int r;
l=-1;r=-1;
par[1]=1;ar[n+n]=-1;
for(int i=2;i<=n+n-1;i++){
if(r<i){
int lit=i;int rit=i;
par[i]=0;
while(lit>=1&&rit<=n+n-1&&ar[lit]==ar[rit]){
par[i]++;lit--;rit++;
}
}else{
par[i]=min(par[l+r-i+1-1],r-i+1)-1;
int lit=i-par[i];int rit=i+par[i];
while(lit>=1&&rit<=n+n-1&&ar[lit]==ar[rit]){
par[i]++;lit--;rit++;
}
}
if(i+par[i]-1>r){
l=i-par[i]+1;
r=i+par[i]-1;
}
}
int ans=0;
for(int i=1;i<=n+n-1;i++){
ans=max(ans,par[i]);
cout<<ar[i]<<" ";
}cout<<endl;
for(int i=1;i<=n+n-1;i++){
cout<<par[i]<<" ";
}cout<<endl;
cout<<"! "<<ans<<endl;
*/
}
