#include <bits/stdc++.h>
using namespace std;
template <typename T>
void read(T &x) {
  x = 0;
  int f = 1;
  char c = getchar();
  for (; !isdigit(c); c = getchar())
    if (c == '-') f = -1;
  for (; isdigit(c); c = getchar()) x = x * 10 + c - '0';
  x = x * f;
}
int n, sav, d[1020], f[1020], cnt, v, ans = -1;
map<int, int> mp;
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> sav;
    d[i] = sav;
    mp[sav]++;
  }
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++) {
      if (i == j) continue;
      if (d[i] == 0 and d[j] == 0) {
        ans = max(ans, mp[0]);
        continue;
      }
      cnt = 2;
      f[1] = d[i];
      f[2] = d[j];
      v = f[1] + f[2];
      mp[d[i]]--;
      mp[d[j]]--;
      while (mp[v] > 0) {
        mp[v]--;
        cnt++;
        f[cnt] = v;
        v = f[cnt - 1] + f[cnt];
      }
      ans = max(cnt, ans);
      for (int k = 1; k <= cnt; k++) mp[f[k]]++;
    }
  cout << ans << endl;
  return 0;
}
