#include <bits/stdc++.h>
using namespace std;
bool f1(pair<long long, long long> x, pair<long long, long long> y) {
  return x.first > y.first;
}
bool f2(pair<long long, long long> x, pair<long long, long long> y) {
  return x.second > y.second;
}
bool f3(long long x, long long y) { return x > y; }
long long gcd(long long x, long long y) {
  if (x == 0) return y;
  return gcd(y % x, x);
}
long long powmod(long long x, long long y, long long m) {
  if (y == 0) return 1;
  long long p = powmod(x, y / 2, m) % m;
  p = (p * p) % m;
  return (y % 2 == 0) ? p : (x * p) % m;
}
long long modif(long long x, long long m) { return (powmod(x, m - 2, m)); }
bool fa(vector<long long> x, vector<long long> y) { return x[0] < y[0]; }
bool fs(vector<long long> x, vector<long long> y) {
  return x.size() > y.size();
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long n;
  cin >> n;
  map<long long, vector<long long> > bb;
  for (int i = 0; i < n; i++) {
    long long x;
    cin >> x;
    bb[x].push_back(i);
  }
  vector<vector<long long> > b;
  for (auto c : bb) {
    b.push_back(c.second);
  }
  long long ans = 0;
  for (int i = 0; i < b.size(); i++) {
    long long j = b[i].size();
    ans = max(ans, j);
    for (int t = 0; t < b.size(); t++) {
      long long l = b[i][0];
      if (i == t) continue;
      long long h = b[t].size();
      ans = max(ans, h);
      for (long long k = 1;; k++) {
        vector<long long>::iterator x;
        if (k % 2 != 0) {
          x = upper_bound(b[t].begin(), b[t].end(), l);
        }
        if (k % 2 == 0) {
          x = upper_bound(b[i].begin(), b[i].end(), l);
        }
        if (k % 2 != 0 &&
            upper_bound(b[t].begin(), b[t].end(), l) == b[t].end()) {
          ans = max(ans, k);
          break;
        }
        if (k % 2 == 0 &&
            upper_bound(b[i].begin(), b[i].end(), l) == b[i].end()) {
          ans = max(ans, k);
          break;
        }
        l = *x;
      }
    }
  }
  cout << ans;
  return 0;
}
