#include <bits/stdc++.h>
using namespace std;
const int maxn = 1010;
unordered_map<int, int> id;
int a[maxn], cnt[maxn];
int cur[maxn], used[maxn];
int it;
bool u[maxn][maxn];
int main() {
  int n;
  cin >> n;
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    if (!id[a[i]]) id[a[i]] = i;
    cnt[id[a[i]]]++;
    if (!a[i]) ans++;
  }
  int res, x, y, tmp;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      if (i == j) continue;
      if (a[i] == 0 && a[j] == 0) continue;
      if (u[id[a[i]]][id[a[j]]]) continue;
      u[id[a[i]]][id[a[j]]] = 1;
      it++;
      cur[id[a[i]]] = cur[id[a[j]]] = 0;
      used[id[a[i]]] = used[id[a[j]]] = it;
      cur[id[a[i]]]++;
      cur[id[a[j]]]++;
      x = a[i], y = a[j];
      res = 2;
      while (1) {
        if (!id[x + y] ||
            (used[id[x + y]] == it && cur[id[x + y]] == cnt[id[x + y]]))
          break;
        res++;
        if (used[id[x + y]] != it) {
          used[id[x + y]] = it;
          cur[id[x + y]] = 0;
        }
        cur[id[x + y]]++;
        tmp = y;
        y += x;
        x = tmp;
      }
      ans = max(ans, res);
    }
  }
  cout << ans;
  return 0;
}
