#include <bits/stdc++.h>
using namespace std;
const int N = 1e3 + 5;
const int MOD = 1e9 + 7;
map<int, int> M, m;
const long long int MAX = 1e9;
long long int A[N];
int n;
void rebuild() {
  M.clear();
  for (int i = 1; i <= n; i++) {
    M[A[i]]++;
  }
}
long long int solve(long long int x, long long int y) {
  long long int cnt = 2;
  long long int c = y;
  long long int ox = x, oy = y;
  M[x]--;
  M[y]--;
  while (abs(c) <= MAX) {
    c = x + y;
    x = y;
    y = c;
    if (M[c]) {
      M[c]--;
      cnt++;
    } else
      break;
  }
  x = ox;
  y = oy;
  M[x]++;
  M[y]++;
  c = x + y;
  int curr = 2;
  while (abs(c) <= MAX) {
    c = x + y;
    x = y;
    y = c;
    if (curr < cnt) {
      curr++;
      M[c]++;
    } else
      break;
  }
  return cnt;
}
int main(int argc, char const *argv[]) {
  cin.sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> A[i];
    M[A[i]]++;
    m[A[i]]++;
  }
  long long int ans = 2;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      if (i == j) continue;
      long long int f = A[i], s = A[j], next = s;
      if ((!f) && (!s)) {
        ans = max(ans, (long long int)M[0]);
        continue;
      }
      long long int now = solve(f, s);
      ans = max(ans, now);
    }
  }
  cout << ans << '\n';
  return 0;
}
