#include <bits/stdc++.h>
using namespace std;
const int N = 1013;
int n;
long long a[N];
map<pair<long long, long long>, int> s;
unordered_map<int, int> used;
unordered_map<int, int> cnt;
int dfs(long long a, long long b) {
  if (used[b] >= cnt[b]) {
    return 0;
  }
  used[b]++;
  int r = dfs(b, a + b);
  used[b]--;
  return r + 1;
}
int main(int argc, char* argv[]) {
  ios_base::sync_with_stdio(0);
  cin >> n;
  int zeros = 0;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    zeros += (a[i] == 0);
    cnt[a[i]]++;
  }
  int res = 0;
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++)
      if (i != j && (a[i] || a[j])) {
        used[a[i]]++;
        res = max(res, 1 + dfs(a[i], a[j]));
        used[a[i]]--;
      }
  cout << max(zeros, res) << endl;
}
