#include <bits/stdc++.h>
using namespace std;
int n, ans = 2, cnt;
int a[1111];
map<int, int> all;
vector<int> used;
inline void solve(int x, int y) {
  long long sum = x + y;
  used.push_back(x), used.push_back(y);
  all[x]--;
  all[y]--;
  cnt = 2;
  while (all[sum]) {
    cnt++;
    all[sum]--;
    used.push_back(sum);
    long long x = sum;
    sum = sum + y;
    y = x;
    ans = max(ans, cnt);
  }
  for (int i = 0; i < (int)used.size(); i++) {
    all[used[i]]++;
  }
  used.clear();
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%I64d", &a[i]);
    all[a[i]]++;
  }
  for (int i = 1; i <= n; i++) {
    for (int j = i + 1; j <= n; j++) {
      if (a[i] == 0 && a[j] == 0)
        ans = max(ans, all[0]);
      else {
        solve(a[i], a[j]);
        solve(a[j], a[i]);
      }
    }
  }
  cout << ans;
  return 0;
}
