#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<to;x++)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
//-------------------------------------------------------

int N;
int A[10101];
int memo[3030][3030];

int dodo(int L,int R) {
	int i,j,k,l,r,x,y; string s;
	if(R<L) return 0;
	if(L==R) return 1;
	if(A[L]==A[R]) return 0;
	
	int& ret=memo[L][R];
	if(ret>=0) return ret;
	ret=2;
	if(A[L]>A[R]) {
		for(i=L+1;i<R;i++) if(A[i]>A[L]) ret=max(ret,1+dodo(L,i));
	}
	else {
		for(i=L+1;i<R;i++) if(A[i]>A[R]) ret=max(ret,1+dodo(i,R));
	}
	return ret;
}

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N;
	FOR(i,N) cin>>A[i];
	int ma=1;
	MINUS(memo);
	FOR(y,N) FOR(x,y) ma=max(ma,dodo(x,y));
	
	cout<<ma<<endl;
	
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false);
	FOR(i,argc-1) s+=argv[i+1],s+='\n';
	FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	solve(); return 0;
}