#include<bits/stdc++.h>
#define int long long
using namespace std;

signed main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int n, u;
    cin >> n >> u;
    vector<int> q(n);
    for(int i = 0; i < n; i++){
        cin >> q[i];
    }
    int ans = -1;
    int a, b, c;
    for(int i = 0; i < n - 2; i++){
        int l = i + 2;
        int r = n;
        while(l + 1 < r){
            int mid = (l + r) / 2;
            if(q[mid] - q[i] <= u){
                l = mid;
            }
            else{
                r = mid;
            }
        }
        if(q[l] - q[i] > u) continue;
        if(ans == -1 || (c - a) * (q[l] - q[i]) < (q[l] - q[i + 1]) * (c - b))
        {
            c = q[l];
            b = q[i];
            a = q[i + 1];
            ans = 0;
        }
    }
    if(ans == -1){
        cout << ans << endl;
    }
    else{
        double x1 = 1.0;
        cout << fixed << setprecision(20) << (c - a) * x1 / (c - b);
    }
    return 0;
}