#include <bits/stdc++.h>
using namespace std;
template <typename T, typename S>
ostream &operator<<(ostream &os, const pair<T, S> &v) {
  os << "(";
  os << v.first << "," << v.second << ")";
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "[";
  long long sz = v.size();
  for (long long i = 0; i < sz; ++i) {
    os << v[i];
    if (i != sz - 1) os << ",";
  }
  os << "]\n";
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const set<T> &v) {
  T last = *v.rbegin();
  os << "[";
  for (auto it : v) {
    os << it;
    if (it != last) os << ",";
  }
  os << "]\n";
  return os;
}
template <typename T, typename S>
ostream &operator<<(ostream &os, const map<T, S> &v) {
  for (auto it : v) {
    os << it.first << " : " << it.second << "\n";
  }
  return os;
}
long long power(long long a, long long b) {
  long long res = 1;
  while (b) {
    if (b % 2) {
      res = (res * a) % 1000000007;
    }
    b /= 2;
    a = (a * a) % 1000000007;
  }
  return res;
}
template <typename Arg1>
void __f(const char *name, Arg1 &&arg1) {
  cerr << name << " : " << arg1 << std::endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
const long long N = 1005;
long long arr[N];
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long n;
  cin >> n;
  for (__typeof(1) i = 1; i <= n; i++) cin >> arr[i];
  unordered_map<long long, long long> cnt;
  for (__typeof(1) i = 1; i <= n; i++) ++cnt[arr[i]];
  long long ans = cnt[0] > 1 ? cnt[0] : 0;
  for (__typeof(1) i = 1; i <= n; i++)
    for (__typeof(i + 1) j = i + 1; j <= n; j++) {
      vector<long long> temp;
      temp.push_back(arr[i]), temp.push_back(arr[j]);
      --cnt[arr[i]], --cnt[arr[j]];
      long long a = arr[i], b = arr[j], curr, len = 2;
      if (a == 0 && b == 0) continue;
      for (;;) {
        curr = a + b;
        if (cnt[curr] == 0) {
          ans = max(ans, len);
          break;
        }
        ++len;
        temp.push_back(curr);
        --cnt[curr];
        a = b;
        b = curr;
      }
      ans = max(ans, len);
      for (auto it : temp) ++cnt[it];
      a = arr[j], b = arr[i], len = 2;
      temp.clear();
      temp.push_back(a), temp.push_back(b);
      --cnt[a], --cnt[b];
      for (;;) {
        curr = a + b;
        if (cnt[curr] == 0) {
          ans = max(ans, len);
          break;
        }
        ++len;
        temp.push_back(curr);
        --cnt[curr];
        a = b;
        b = curr;
      }
      ans = max(ans, len);
      for (auto it : temp) ++cnt[it];
    }
  cout << ans << endl;
  return 0;
}
