#include <bits/stdc++.h>
using namespace std;
long long a[1010];
int main() {
  ios::sync_with_stdio(false);
  map<long long, int> x;
  long long n;
  cin >> n;
  long long totzero = 0;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    x[a[i]]++;
    if (a[i] == 0) totzero++;
  }
  long long mm = 0;
  map<pair<long long, long long>, bool> qq;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (i != j && !qq[make_pair(a[i], a[j])]) {
        qq[make_pair(a[i], a[j])] = 1;
        map<long long, int> used;
        if (a[i] == 0 && a[j] == 0) {
          mm = max(mm, totzero);
          continue;
        }
        long long t = a[i] + a[j];
        used[a[i]]++;
        used[a[j]]++;
        int v = a[j];
        long long r = 2;
        while (x[t] != 0 && used[t] < x[t]) {
          used[t]++;
          int w = t;
          t += v;
          v = w;
          r++;
        }
        mm = max(mm, r);
      }
    }
  }
  cout << mm;
}
