#include <bits/stdc++.h>
using namespace std;
long long a[1005];
unordered_map<long long, int> mp;
long long t[105], cnt;
int main() {
  mp.max_load_factor(0.1);
  mp.reserve(262144);
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%I64d", &a[i]);
  for (int i = 0; i < n; i++) mp[a[i]]++;
  int res = 2;
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++) {
      if (i == j) continue;
      if (a[i] == 0 && a[j] == 0)
        res = max(res, mp[0]);
      else {
        t[0] = a[i];
        t[1] = a[j];
        long long now = t[0] + t[1];
        cnt = 2;
        while (abs(now) <= 1000000000) {
          t[cnt++] = now;
          now = t[cnt - 2] + t[cnt - 1];
        }
        t[cnt++] = now;
        mp[t[0]]--;
        mp[t[1]]--;
        for (int k = 2; k < cnt; k++) {
          if (mp.find(t[k]) == mp.end() || mp[t[k]] == 0) {
            res = max(res, k);
            for (int tt = 0; tt < k; tt++) mp[t[tt]]++;
            break;
          } else
            mp[t[k]]--;
        }
      }
    }
  printf("%d\n", res);
  return 0;
}
