#include <bits/stdc++.h>
using namespace std;
inline void pisz(int n) { printf("%d\n", n); }
template <typename T, typename TT>
ostream& operator<<(ostream& s, pair<T, TT> t) {
  return s << "(" << t.first << "," << t.second << ")";
}
template <typename T>
ostream& operator<<(ostream& s, vector<T> t) {
  for (int(i) = 0; (i) < (((int)((t).size()))); ++(i)) s << t[i] << " ";
  return s;
}
int main() {
  int(n);
  scanf("%d", &(n));
  set<int> distinct;
  unordered_map<int, int> m;
  for (int(i) = 0; (i) < (n); ++(i)) {
    int(x);
    scanf("%d", &(x));
    m[x]++;
    distinct.insert(x);
  }
  int ma = 2;
  for (int a0 : distinct)
    for (int b0 : distinct) {
      if (a0 == b0 && m[a0] < 2) continue;
      int len = 2;
      int a = a0, b = b0;
      --m[a];
      --m[b];
      while (1) {
        int c = a + b;
        unordered_map<int, int>::iterator it = m.find(c);
        if (it == m.end() || it->second < 1) break;
        --it->second;
        ++len;
        a = b;
        b = c;
      }
      (ma) = max((ma), (len));
      ;
      a = a0;
      b = b0;
      ++m[a];
      ++m[b];
      for (int(k) = (3); (k) <= (len); ++k) {
        int c = a + b;
        m[c]++;
        a = b;
        b = c;
      }
    }
  pisz(ma);
}
