#include <bits/stdc++.h>
using namespace std;
int n, maxi = 2, ans = 2;
int a[100005];
vector<int> num;
int main() {
  cin >> n;
  for (int i = 0; i < n; i++) cin >> a[i];
  if (n < 3) {
    cout << n;
    return 0;
  }
  for (int i = 2; i < n; i++) {
    if (a[i] == a[i - 1] + a[i - 2]) {
      ans++;
      maxi = max(maxi, ans);
    } else
      ans = 2;
  }
  cout << maxi;
  return 0;
}
