#include <bits/stdc++.h>
using namespace std;
const int N = 1e3 + 2;
int n;
int a[N];
map<int, int> m;
map<pair<int, int>, bool> checked;
int main() {
  cin >> n;
  int zero = 0;
  for (int i = 0; i < n; ++i) {
    scanf("%d", a + i);
    if (!a[i]) zero++;
    ;
    m[a[i]]++;
  }
  sort(a, a + n);
  int ans = -1;
  int help1, help2, help3;
  for (int i = 0; i < n; ++i)
    for (int j = 0; j < n; ++j)
      if (i != j) {
        if (!a[i] and (!a[j])) continue;
        if (checked[make_pair(a[i], a[j])]) continue;
        checked[make_pair(a[i], a[j])] = true;
        map<int, int> m1;
        help3 = 2;
        m1[a[i]]++, m1[a[j]]++;
        help1 = a[i];
        help2 = a[j];
        while (m1[help1 + help2] < m[help1 + help2]) {
          m1[help1 + help2]++;
          help3++;
          help2 += help1;
          help1 = help2 - help1;
        }
        ans = max(ans, help3);
      }
  ans = max(ans, zero);
  cout << ans;
}
