#include <bits/stdc++.h>
using namespace std;
const int N = 40;
void solve() {
  int n;
  cin >> n;
  unordered_set<int> st;
  set<int> pr;
  unordered_map<int, int> col;
  int ans = 0;
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    if (col.find(x) == col.end()) {
      col[x] = 0;
    }
    col[x]++;
    if (x == 0) {
      ans++;
    }
    pr.insert(x);
    st.insert(x);
  }
  vector<int> a;
  while (!pr.empty()) {
    a.push_back(*pr.begin());
    pr.erase(*pr.begin());
  }
  n = a.size();
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      unordered_map<int, int> col2;
      int f = a[i];
      int s = a[j];
      if (col2.find(s) == col2.end()) {
        col2[s] = 0;
      }
      if (col2.find(f) == col2.end()) {
        col2[f] = 0;
      }
      col2[f]++;
      col2[s]++;
      if (col[s] < col2[s]) {
        continue;
      }
      int tmp = 2;
      while (1) {
        int sm = f + s;
        if (col2.find(sm) == col2.end()) {
          col2[sm] = 0;
        }
        if (st.count(sm) == 0 || col[sm] <= col2[sm]) {
          break;
        }
        col2[sm]++;
        tmp++;
        f = s;
        s = sm;
      }
      ans = max(ans, tmp);
    }
  }
  cout << ans;
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  solve();
}
