#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  long long int arr[n];
  unordered_map<long long int, long long int> u;
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
    u[arr[i]]++;
  }
  long long int ans = 0, cnt = 0;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (i != j) {
        long long int a = arr[i], b = arr[j];
        if (a == 0 && b == 0) {
          ans = max(ans, u[0]);
          break;
        } else {
          cnt = 2;
          u[arr[i]]--;
          u[arr[j]]--;
          while (1) {
            long long int x = u[a + b];
            if (x > 0) {
              u[a + b]--;
              cnt++;
              long long int temp = b;
              b += a;
              a = temp;
            } else
              break;
          }
          u[b]++;
          u[a]++;
          long long int y = cnt - 2;
          while (y > 0) {
            u[b - a]++;
            long long int temp = a;
            a = b - a;
            b = temp;
            y--;
          }
        }
      }
      ans = max(ans, cnt);
    }
  }
  cout << ans;
  return 0;
}
