#include<bits/stdc++.h>
#define int long long
using namespace std;
void ts(){cout<<"IAKIOI\n";}
inline int read(){
	int n=0,f=1,ch=getchar();
	while(ch<'0'||ch>'9'){
		if(ch=='-')f=-1;
		ch=getchar();
	}
	while(ch>='0'&&ch<='9'){
		n=n*10+ch-'0';
		ch=getchar();
	}
	return n*f;
}
int n;
int a[500005];
int dp[2][505][505];
signed main(){
	n=read();
	for(int i=1;i<=n;i++)a[i]=read();
	memset(dp,-0x3f,sizeof(dp));
	dp[1][a[1]][0]=1;
	for(int i=2;i<=n;i++){
		int lst=(i&1)^1;
		int cur=i&1;
		for(int j=1;j<=n;j++){
			for(int k=0;k<=n;k++){
				if(dp[lst][j][k]<0)continue;
				if(a[i]>j){
					dp[cur][a[i]][j]=max(dp[cur][a[i]][j],dp[lst][j][k]+1);
				}
				else{
					dp[cur][j][k]=max(dp[cur][j][k],dp[lst][j][k]);
					if(a[i]>k){
						dp[cur][a[i]][k]=max(dp[cur][a[i]][k],dp[lst][j][k]);
					}
				}
			}
		}
		for(int j=1;j<=n;j++)for(int k=0;k<=n;k++)dp[lst][j][k]=-(1ll<<60);
	}
	int res=0;
	for(int i=1;i<=n;i++){
		for(int j=0;j<=n;j++)res=max(res,dp[n&1][i][j]);
	}
	cout<<res<<"\n";
	return 0;
}
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