#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  int n;
  cin >> n;
  vector<int> a(n);
  map<int, int> m;
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
    ++m[a[i]];
  }
  int ans = 2;
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n; ++j) {
      if (i != j) {
        if (!a[i] && !a[j]) {
          ans = max(ans, m[0]);
          continue;
        }
        vector<int> f(2);
        f[0] = a[i], f[1] = a[j];
        --m[f[0]], --m[f[1]];
        while (auto &cnt = m[f[f.size() - 1] + f[f.size() - 2]]) {
          f.push_back(f[f.size() - 1] + f[f.size() - 2]);
          --cnt;
        }
        ans = max(ans, (int)f.size());
        for (int i : f) {
          ++m[i];
        }
      }
    }
  }
  cout << ans << endl;
  return 0;
}
