#include <bits/stdc++.h>
using namespace std;
long long int MOD(long long int a, long long int b) {
  if (a > b)
    return a - b;
  else
    return b - a;
}
long long int power(long long int x, long long int y, long long int p) {
  long long int res = 1;
  x = x % p;
  while (y > 0) {
    if (y & 1) res = (res * x) % p;
    y = y >> 1;
    x = (x * x) % p;
  }
  return res;
}
long long int logg(long long int a) {
  long long int x = 0;
  while (a > 1) {
    x++;
    a /= 2;
  }
  return x;
}
bool isGreater(pair<long long int, long long int> a,
               pair<long long int, long long int> b) {
  if (a.first * b.second > b.first * a.second)
    return true;
  else
    return false;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  int n;
  long long int U;
  cin >> n >> U;
  vector<long long int> A(n);
  for (int i = 0; i < n; i++) cin >> A[i];
  pair<long long int, long long int> m = make_pair(-1, -1);
  for (int i = 0; i < n - 2; i++) {
    int t = upper_bound(A.begin() + i + 2, A.end(), A[i] + U) - A.begin() - 1;
    if (t == i + 1)
      continue;
    else {
      if (m == make_pair((long long int)-1, (long long int)-1)) {
        m = make_pair(A[t] - A[i + 1], A[t] - A[i]);
      } else {
        if (isGreater(make_pair(A[t] - A[i + 1], A[t] - A[i]), m))
          m = make_pair(A[t] - A[i + 1], A[t] - A[i]);
      }
    }
  }
  if (m == make_pair((long long int)-1, (long long int)-1))
    cout << -1;
  else {
    cout.precision(11);
    cout << fixed << ((long double)(1.0 * m.first)) / m.second;
  }
}
