using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Collections.Generic;
using System.Diagnostics;
using System.Numerics;
using Enu = System.Linq.Enumerable;

class Program
{
    public void Solve()
    {
        int N = Reader.Int(), L = Reader.Int() * 60;
        var A = Reader.StringArray(N).Select(s =>
                (int)TimeSpan.Parse("0:" + s).TotalSeconds).ToArray();
        if (A.Sum() - A.Min() < L) { Console.WriteLine(N); return; }

        var dp = new double[N + 1, L + 1];
        dp[0, 0] = 1;
        for (int i = 0; i < N; i++)
            for (int num = i; num >= 0; num--)
                for (int len = 0; len + A[i] < L; len++)
                    dp[num + 1, len + A[i]] += dp[num, len];

        var fact = new double[N + 1];
        fact[0] = 1;
        for (int i = 1; i <= N; i++) fact[i] = fact[i - 1] * i;
        var others = new double[N + 1, L + 1];
        double ans = 0;

        for (int i = 0; i < N; i++)
            for (int num = 0; num < N; num++)
            {
                double sum = 0;
                for (int len = 0; len < L; len++)
                {
                    others[num, len] = dp[num, len];
                    if (num > 0 && len >= A[i]) others[num, len] -= others[num - 1, len - A[i]];
                    sum += others[num, len];
                }
                ans += sum * fact[num] * fact[N - num - 1];
            }
        ans /= fact[N];

        Console.WriteLine(ans);
        Console.ReadLine();
    }
}


class Entry { static void Main() { new Program().Solve(); } }
class Reader
{
    private static TextReader reader = Console.In;
    private static readonly char[] separator = { ' ' };
    private static readonly StringSplitOptions op = StringSplitOptions.RemoveEmptyEntries;
    private static string[] A = new string[0];
    private static int i;
    private static void Init() { A = new string[0]; }
    public static void Set(TextReader r) { reader = r; Init(); }
    public static void Set(string file) { reader = new StreamReader(file); Init(); }
    public static bool HasNext() { return CheckNext(); }
    public static string String() { return Next(); }
    public static int Int() { return int.Parse(Next()); }
    public static long Long() { return long.Parse(Next()); }
    public static double Double() { return double.Parse(Next()); }
    public static int[] IntLine() { return Array.ConvertAll(Split(Line()), int.Parse); }
    public static int[] IntArray(int N) { return Enu.Range(0, N).Select(i => Int()).ToArray(); }
    public static int[][] IntTable(int H) { return Enu.Range(0, H).Select(i => IntLine()).ToArray(); }
    public static string[] StringArray(int N) { return Enu.Range(0, N).Select(i => Next()).ToArray(); }
    public static string Line() { return reader.ReadLine().Trim(); }
    private static string[] Split(string s) { return s.Split(separator, op); }
    private static string Next() { CheckNext(); return A[i++]; }
    private static bool CheckNext()
    {
        if (i < A.Length) return true;
        string line = reader.ReadLine();
        if (line == null) return false;
        if (line == "") return CheckNext();
        A = Split(line);
        i = 0;
        return true;
    }
}