#include <bits/stdc++.h>
using namespace std;
int n, a[1001], ans, i, j, x;
map<int, int> m;
map<pair<int, int>, bool> used;
vector<int> v;
int main() {
  scanf("%d", &n);
  for (i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    m[a[i]]++;
  }
  for (i = 1; i <= n; i++) {
    for (j = 1; j <= n; j++) {
      if (i == j) continue;
      if (used[make_pair(a[i], a[j])]) continue;
      used[make_pair(a[i], a[j])] = true;
      m[a[i]]--;
      m[a[j]]--;
      v.push_back(a[i]);
      v.push_back(a[j]);
      x = a[i] + a[j];
      while (m[x]) {
        m[x]--;
        v.push_back(x);
        x += v[v.size() - 2];
      }
      ans = max(ans, (int)v.size());
      while (!v.empty()) {
        m[v.back()]++;
        v.pop_back();
      }
    }
  }
  cout << ans << endl;
}
