#include <bits/stdc++.h>
using namespace std;
const int oo = 0x3f3f3f3f;
const long long ooo = 9223372036854775807ll;
const int _cnt = 1000 * 1000 + 7;
const int _p = 1000 * 1000 * 1000 + 7;
const int N = 100005;
const double PI = acos(-1.0);
const double eps = 1e-9;
int o(int x) { return x % _p; }
int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }
int lcm(int a, int b) { return a / gcd(a, b) * b; }
void file_put() {
  freopen("filename.in", "r", stdin);
  freopen("filename.out", "w", stdout);
}
int n, E[N], q[N], U, rr, l0;
double l = 0, r = 1, mid, ans;
double h(int k, double m) { return (E[k] - E[k - 1] * m) / (1 - m); }
bool check(double m) {
  rr = 0, l0 = 1;
  q[++rr] = 2;
  for (int k = (3); k <= (n); ++k) {
    while (rr >= l0 && E[k] - E[q[l0] - 1] > U) ++l0;
    if (rr >= l0)
      if (h(q[l0], m) <= E[k]) return 1;
    double t = h(k, m);
    while (rr >= l0 && h(q[rr], m) > t) rr--;
    q[++rr] = k;
  }
  return 0;
}
int main() {
  scanf("%d%d", &n, &U);
  for (int i = (1); i <= (n); ++i) scanf("%d", &E[i]);
  if (!check(0)) return 0 * printf("-1\n");
  for (int i = (1); i <= (100); ++i) {
    mid = (l + r) / 2;
    if (check(mid))
      ans = mid, l = mid;
    else
      r = mid;
  }
  printf("%.15lf\n", ans);
  return 0;
}
