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

class Program
{
    void Solve()
    {
        int N = reader.Int(), L = reader.Int() * 60;
        var S = Enu.Range(0, N).Select(i => reader.String()).ToArray();
        var Sec = S.Select(s => int.Parse(s.Substring(0, 2)) * 60 + int.Parse(s.Substring(3))).ToArray();
        int[] sumSec = new int[N];
        for (int i = 0; i < N; i++) sumSec[i] = Sec[i] + (i > 0 ? sumSec[i - 1] : 0);
        if (sumSec[N - 1] <= L) { Console.WriteLine(N); return; }

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

        for (int i = 0; i < N; i++)
        {
            var dp = new long[N + 1, sumSec[N - 1] + 1];
            dp[0, 0] = 1;
            for (int other = 0; other < N; other++)
                if (other != i)
                    for (int used = other; used >= 0; used--)
                        for (int len = 0; len + Sec[other] <= sumSec[other]; len++)
                            dp[used + 1, len + Sec[other]] += dp[used, len];
            double bad = 0;
            for (int used = 1; used <= N - 1; used++)
                for (int len = L; len <= sumSec[N - 1]; len++)
                    bad += dp[used, len] * fact[used] * fact[N - used - 1] / fact[N];
            ans += 1 - bad;
        }

        Console.WriteLine(ans);
    }


    Reader reader = new Reader(Console.In);
    static void Main() { new Program().Solve(); }
}

class Reader
{
    private readonly TextReader reader;
    private readonly char[] separator = { ' ' };
    private readonly StringSplitOptions removeOp = StringSplitOptions.RemoveEmptyEntries;
    private string[] A = new string[0];
    private int i;

    public Reader(TextReader r) { reader = r; }
    public bool HasNext() { return Enqueue(); }
    public string String() { return Dequeue(); }
    public int Int() { return int.Parse(Dequeue()); }
    public long Long() { return long.Parse(Dequeue()); }
    public double Double() { return double.Parse(Dequeue()); }
    public int[] IntLine() { var s = Line(); return s == "" ? new int[0] : Array.ConvertAll(Split(s), int.Parse); }
    public int[] IntArray(int N) { return Enu.Range(0, N).Select(i => Int()).ToArray(); }
    public int[][] IntGrid(int H) { return Enu.Range(0, H).Select(i => IntLine()).ToArray(); }
    public string[] StringLine(int N) { return Enu.Range(0, N).Select(i => Line()).ToArray(); }
    public string Line() { return reader.ReadLine().Trim(); }
    private string[] Split(string s) { return s.Split(separator, removeOp); }
    private bool Enqueue()
    {
        if (i < A.Length) return true;
        string line = reader.ReadLine();
        if (line == null) return false;
        if (line == "") return Enqueue();
        A = Split(line);
        i = 0;
        return true;
    }
    private string Dequeue() { Enqueue(); return A[i++]; }
}