#include <bits/stdc++.h>
using namespace std;
const int Mxn = 4005;
int a[Mxn], b[Mxn];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) cin >> a[i], b[i] = a[i];
  sort(b, b + n);
  map<int, int> m;
  int cnt = 0;
  for (int i = 0; i < n; i++) {
    if (m.count(b[i])) continue;
    m[b[i]] = cnt++;
  }
  for (int i = 0; i < n; i++) a[i] = m[a[i]];
  int ans = 1;
  for (int i = 0; i < n; i++) {
    int lst[n], r[n];
    memset(lst, -1, sizeof lst);
    memset(r, 0, sizeof r);
    int cntp = 1, lstp = i;
    for (int j = i + 1; j < n; j++) {
      if (a[j] == a[i]) {
        cntp++, lstp = j;
      } else {
        if (lst[a[j]] == -1)
          r[a[j]] = 2;
        else if (lst[a[j]] < lstp)
          r[a[j]] += 2;
        lst[a[j]] = j;
      }
    }
    int mx = 0;
    for (int i = 0; i < n; i++) {
      if (lst[i] == -1) continue;
      if (lst[i] < lstp)
        mx = max(mx, r[i] + 1);
      else
        mx = max(mx, r[i]);
    }
    ans = max(ans, max(mx, cntp));
  }
  cout << ans << '\n';
  return 0;
}
