#include <bits/stdc++.h>
using namespace std;
const int MAX = 1010;
int arr[MAX], n;
unordered_map<int, int> mp;
set<pair<int, int> > ss;
int solve(int a, int b) {
  auto &it = mp[b];
  it--;
  if (!mp[a + b]) return it++, 2;
  int ret = 1 + solve(b, a + b);
  it++;
  return ret;
}
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    scanf("%d", arr + i);
    mp[arr[i]]++;
  }
  int ans = 0;
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++)
      if (i != j && ss.insert({arr[i], arr[j]}).second) {
        auto &it = mp[arr[i]];
        it--;
        ans = max(ans, solve(arr[i], arr[j]));
        it++;
      }
  printf("%d\n", ans);
  return 0;
}
