#include <bits/stdc++.h>
using namespace std;
inline long long mi(long long a, long long b) { return ((a - b > 0) ? b : a); }
inline double ma(double a, double b) { return a > b ? a : b; }
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  cerr << name << " : " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
long long ar[200010];
inline double check(long long k, long long x, long long y, long long p) {
  long long val1 = k * (x - y);
  long long val2 = (p - y) * (p - y);
  val2 += k * (p - y);
  double xd = (val1 * 1.0) / (val2 * 1.0);
  return xd;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  ;
  long long n, u;
  cin >> n >> u;
  vector<long long> v;
  for (int(i) = (0); (i) < (n); (i)++) cin >> ar[i], v.push_back(ar[i]);
  double froz = 0.0;
  for (int(i) = (0); (i) < (n - 2); (i)++) {
    long long y = ar[i], x = ar[i + 1], p = ar[i + 2];
    long long mx = ar[i] + u;
    long long id = upper_bound((v).begin(), (v).end(), mx) - v.begin();
    long long ini = i + 2, fin = id - 1;
    if (ini <= fin) {
      for (int(j) = (0); (j) < (70); (j)++) {
        long long l = ini + (fin - ini) / 3, r = fin - (fin - ini) / 3;
        long long val1 = ar[l], val2 = ar[r];
        if (check(val1 - p, x, y, p) < check(val2 - p, x, y, p))
          ini = l;
        else
          fin = r;
      }
      long long lel = ini;
      if (check(ar[fin] - p, x, y, p) > check(ar[ini] - p, x, y, p)) lel = fin;
      double fs = ma(check(ar[fin] - p, x, y, p), check(ar[ini] - p, x, y, p));
      froz = ma(froz, fs + ((p - x) * 1.0) / (1.0 * (p - y)));
    }
  }
  if (froz == 0.0)
    cout << -1 << endl;
  else
    cout << fixed << setprecision(11) << froz << endl;
  return 0;
}
