#include <bits/stdc++.h>
using namespace std;
int n;
long long a[1010];
long long ans;
long long vis[1010];
map<long long, long long> mp;
void dfs(long long x, long long y, long long cnt) {
  ans = max(cnt, ans);
  if (mp[x + y]) {
    mp[x + y]--;
    dfs(y, x + y, cnt + 1);
    mp[x + y]++;
  }
}
int main() {
  while (cin >> n) {
    for (int i = 1; i <= n; i++) cin >> a[i];
    for (int i = 1; i <= n; i++) mp[a[i]]++;
    long long kk = 0;
    for (int i = 1; i <= n; i++)
      if (a[i] == 0) kk++;
    ans = 0;
    for (int i = 0; i <= n; i++) vis[i] = 0;
    for (int i = 1; i <= n; i++) {
      for (int j = 1; j <= n; j++) {
        if (i != j) {
          if (a[i] == 0 && a[j] == 0) {
            ans = max(ans, kk);
            continue;
          }
          mp[a[i]]--;
          mp[a[j]]--;
          dfs(a[i], a[j], 2);
          mp[a[i]]++, mp[a[j]]++;
        }
      }
    }
    cout << ans << endl;
  }
  return 0;
}
