#include <bits/stdc++.h>
using namespace std;
map<int, int> mp;
int a[1001], ans;
int cnt;
int t;
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    mp[a[i]]++;
  }
  sort(a + 1, a + 1 + n);
  ans = 2;
  ans = max(mp[0], ans);
  int a1, a2;
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++) {
      if ((long long)i == j) continue;
      if (a[i] == 0 && a[j] == 0) continue;
      if (i > 1 && a[i] == a[i - 1]) break;
      map<int, int> mp2;
      mp2[a[i]]++, mp2[a[j]]++;
      cnt = 2;
      a1 = a[i], a2 = a[j];
      while (++mp2[a1 + a2] <= mp[a1 + a2]) {
        cnt++, t = a1;
        a1 = a2, a2 += t;
      }
      ans = max(ans, cnt);
    }
  printf("%d", ans);
  return 0;
}
