#include <bits/stdc++.h>
using namespace std;
const long long int mod = 1000000007;
map<long long int, long long int> counts;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int n;
  cin >> n;
  long long int arr[n];
  for (long long int i = 0; i < n; i++) {
    cin >> arr[i];
    counts[arr[i]] = 0;
  }
  for (long long int i = 0; i < n; i++) counts[arr[i]]++;
  long long int ans = 0, a, b, c;
  for (long long int i = 0; i < n; i++) {
    for (long long int j = 0; j < n; j++) {
      if (i == j) continue;
      a = arr[i], b = arr[j];
      if (!a and !b) {
        ans = max(ans, counts[a]);
        continue;
      }
      vector<long long int> repair;
      repair.push_back(a);
      repair.push_back(b);
      counts[a]--;
      counts[b]--;
      while (1) {
        c = a + b;
        if (counts.find(c) != counts.end() and counts[c] > 0) {
          counts[c]--;
          repair.push_back(c);
          a = b;
          b = c;
        } else
          break;
      }
      ans = max(ans, (long long int)repair.size());
      for (auto it : repair) counts[it]++;
    }
  }
  cout << ans << endl;
  return 0;
}
