#include <bits/stdc++.h>

using namespace std;

typedef long long int ll;
typedef double ld;

typedef pair<ll, ll> ii;
typedef vector<ll> vi;
typedef vector<ii> vii;

#define PB push_back
#define FOR(prom, a, b) for ( ll prom = (a); prom < (ll)(b); ++prom )
#define F(a) FOR(i,0,a)
#define FF(a) FOR(j,0,a)

#define EPS (1e-10)

int q[5001][5001];

int main () {
	ios::sync_with_stdio(false);
	ll N;
	while(cin>>N){
		vi aa(N),a(N);
		F(N)cin>>aa[i];
		map<ll,ll> m;
		ll idx=0;
		F(N){
			auto it=m.find(aa[i]);
			ll r;
			if(it==m.end()){
				r=m[aa[i]]=idx++;
			}else{
				r=it->second;
			}
			a[i]=r;
		}
//		F(N)cout<<a[i]<<' ';
	//	cout<<endl;
		F(N)FF(N)q[i][j]=-1;
		FOR(i,1,N){
			for(int j=i-1; j>=0; --j){
				q[i][j]=max(q[i-1][j], q[i][j+1]);
				if(a[i]==a[j])q[i][j]=max(q[i][j], q[i-1][j+1]+1);
			}
		}
		cout<<q[N-1][0]+1<<endl;
	}
	return 0;
}