#include <bits/stdc++.h>
#include <unordered_map>

using namespace std;


unordered_map<int, int> memory;
vector<int> ducks;

int solve_interval(int from, int to) {
	int p = from + 20000 * to;
	if (!(from < to))
		return 0;
	if (memory.count(p) > 0)
		return memory[p];

	unordered_map<int, int> right_most;
	for (int i = from; i < to; ++i) {
		right_most[ducks[i]] = i;
	}

	int current_right = 0;
	int best = -1;
	for (int i = from; i < to; ++i) {
		if (current_right < i)
			current_right = i;
		if (right_most[ducks[i]] <= current_right)
			continue;
		//cout << i << ' ' << ducks[i] << ' ' << right_most.count(ducks[i]) << endl;
		current_right = right_most[ducks[i]];
		int sol = solve_interval(i+1, right_most[ducks[i]]);
		if (sol > best)
			best = sol;
	}
	memory[p] = best+1;
	return best+1;
}

int main() {
	int N, i, d;
	while (cin >> N) {
		memory.clear();
		ducks.clear();
		for (i = 0; i < N; ++i) {
			cin >> d;
			ducks.push_back(d);
		}
		cout << solve_interval(0, N) << '\n';
	}
}