#include <bits/stdc++.h>
using namespace std;
int n, a[2001], ans, f[2001];
map<int, int> mp;
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    mp[a[i]]++;
  }
  sort(a + 1, a + n + 1);
  ans = max(ans, mp[0]);
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      if (j > 1 && a[j] == a[j - 1]) continue;
      if (i != j) {
        int f1, f2, sum, w;
        if (!a[i] && !a[j]) {
          continue;
        }
        map<int, int> mp2;
        sum = 2;
        mp2[a[i]]++;
        mp2[a[j]]++;
        f1 = a[i];
        f2 = a[j];
        while (++mp2[w = f1 + f2] <= mp[f1 + f2]) {
          sum++;
          f1 = f2;
          f2 = w;
        }
        ans = max(ans, sum);
      }
    }
  }
  printf("%d\n", ans);
  return 0;
}
