#include <bits/stdc++.h>
using namespace std;
int l, a[1001], b[1001], c[1001], g[1001], m, v, y, ans;
map<int, int> f;
int main() {
  cin >> l;
  for (int i = 1; i <= l; i++) {
    scanf("%d", &a[i]);
    f[a[i]]++;
  }
  sort(a + 1, a + l + 1);
  for (int i = 1; i <= l; i++) {
    for (int j = 1; j <= l; j++) {
      if (i != j) {
        if (i > 1 && a[i - 1] == a[i]) break;
        if (a[i] == 0 && a[j] == 0) {
          ans = max(ans, f[0]);
          continue;
        }
        map<int, int> d;
        g[1] = a[i];
        g[2] = a[j];
        d[g[1]]++;
        d[g[2]]++;
        y = 2;
        while (d[g[y] + g[y - 1]] < f[g[y] + g[y - 1]]) {
          y++;
          g[y] = g[y - 1] + g[y - 2];
          d[g[y]]++;
        }
        ans = max(ans, y);
      }
    }
  }
  cout << ans;
}
