#include<bits/stdc++.h>
using namespace std;
int a[200010];
vector<int>v[200010];
unordered_map<int,int>mp;
int main(){
	int n;
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i];
	}
	int l=0;
	int id=0;
	for(int i=1;i<=n;i++){
		if(i==1 || a[i]==a[i-1]){
			l++;
		}
		//cout<<l<<endl;
		if((a[i]!=a[i-1] && i!=1)|| i==n){
			//cout<<i<<" "<<l<<endl;
			if(l<=1 && !v[id].empty()){
				id++;
			}
			if(l>2){
				v[id].push_back(a[i-1]);
				++id;
				v[id].push_back(a[i-1]); 
			}
			if(l==2){
				v[id].push_back(a[i-1]);
			}
			l=1;
		} 
		//cout<<l<<endl;
	}
	int ans=0;
	for(int i=0;i<=id;i++){
		int len=v[i].size();
		//cout<<len<<endl;
		mp.clear();
		deque<int>q;
		q.clear();
		for(int j=0;j<len;j++){
			q.push_back(v[i][j]);
			if(mp[v[i][j]]==1){
				while(!q.empty()){
					int tp=q.front();q.pop_front();
					if(tp==v[i][j]){
						break;
					}
				}
			}
			mp[v[i][j]]=1;
			
		}
		int p=(q.size())*2;
		ans=max(p,ans); 
	}
	cout<<ans;
} 
/*11 1122 2211
  */

思路是分成小块再求值

wa 了18个