#include <bits/stdc++.h>
#pragma GCC optimize(2)
using namespace std;
const int mod = 1e9 + 7;
const double eps = 1e-6;
const int N = 1e3 + 7;
int a[N], f[N];
map<int, int> mp;
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i <= n - 1; i++) {
    scanf("%d", &a[i]);
    mp[a[i]]++;
  }
  int res = 0;
  for (int i = 0; i <= n - 1; i++)
    for (int j = 0; j <= n - 1; j++)
      if (i != j) {
        if (!a[i] && !a[j]) {
          res = max(res, mp[0]);
          continue;
        }
        f[1] = a[i], f[2] = a[j];
        int c = 2, f1 = a[i], f2 = a[j], w = f1 + f2;
        mp[f1]--;
        mp[f2]--;
        while (mp[w]) {
          mp[w]--;
          f[++c] = w;
          f1 = f2;
          f2 = w;
          w = f1 + f2;
        }
        res = max(res, c);
        for (int i = 1; i <= c; i++) mp[f[i]]++;
      }
  printf("%d\n", res);
  return 0;
}
