#include <bits/extc++.h>

using ll = long long;

template <class T>
std::istream& operator>>(std::istream& is, std::vector<T>& xs) {
  for (T& x : xs) is >> x;
  return is;
}

int main() {
  int N;
  std::cin >> N;
  std::vector<ll> S(N);
  std::cin >> S;

  std::vector<ll> zts = S;

  std::sort(zts.begin(), zts.end());
  zts.erase(std::unique(zts.begin(), zts.end()), zts.end());

  int M = zts.size();

  for (ll& x : S) {
    x = std::lower_bound(zts.begin(), zts.end(), x) - zts.begin();
  }

  std::vector<int> back(N, -1);
  {
    std::vector<int> tmp(M, -1);
    for (int i = 0; i < N; i++) {
      back[i] = tmp[S[i]];
      tmp[S[i]] = i;
    }
  }

  std::vector<int> dp(N + 1, 0);
  std::vector<int> dpsame(N, 0);

  for (int i = 0; i < N; i++) {
    int k = back[i];
    if (k == -1) continue;

    dpsame[i] = dp[k] + 2;
    dp[i + 1] = std::max(dpsame[k] + 1, dpsame[i]);
  }

  std::cout << dp[N] << std::endl;
}