// URL: https://yukicoder.me/problems/no/155

import std.algorithm, std.array, std.bitmanip, std.container, std.conv, std.format,
       std.functional, std.math, std.range, std.traits, std.typecons, std.stdio, std.string;

version(unittest) {} else
void main()
{
  int N, L; io.getV(N, L);
  string[] st; io.getA(N, st);

  L *= 60;
  auto S = st.map!(sti => sti[0..2].to!int*60+sti[3..5].to!int).array;

  if (S.sum < L) io.put!"{exit: true}"(N);

  auto dp1 = new long[][][](N+1, N+1, L); dp1[0][0][0] = 1;
  foreach (i, Si; S)
    foreach (j; 0..N+1)
      foreach (k; 0..L) {
        dp1[i+1][j][k] = dp1[i][j][k];
        if (j >= 1 && k >= Si)
          dp1[i+1][j][k] += dp1[i][j-1][k-Si];
      }

  auto fact = Fact!(double, false)(N+1);

  auto r = 0.0, dp2 = new long[][](N+1, L);
  foreach (i, Si; S) {
    foreach (j; 0..N+1)
      foreach (k; 0..L) {
        dp2[j][k] = dp1[N][j][k];
        if (j >= 1 && k >= Si)
          dp2[j][k] -= dp2[j-1][k-Si];
      }

    foreach (j; 0..N)
      foreach (k; max(0, L-Si)..L)
        r += dp2[j][k]*fact[j+1]*fact[N-1-j];
  }

  io.put(r/fact[N]);
}

struct Fact(T, bool inv = true)
{
  int n;
  T[] table;
  alias table this;
  static if (inv) T[] invTable;

  pure nothrow @safe
  {
    this(int n)
    {
      this.n = n;

      table = new T[](n+1); table[0] = 1;
      foreach (i; 1..n+1) table[i] = table[i-1]*i;

      static if (inv) {
        invTable = new T[](n+1); invTable[n] = T(1)/table[n];
        foreach_reverse (i; 1..n+1) invTable[i-1] = invTable[i]*i;
      }
    }
  }

  pure nothrow @nogc @safe
  {
    static if (inv) {
      T perm(size_t a, size_t b)
        in { assert(n >= a && a >= b); }
      do
      {
        return table[a]*invTable[a-b];
      }

      T combi(size_t a, size_t b)
        in { assert(n >= a && a >= b); }
      do
      {
        return table[a]*invTable[b]*invTable[a-b];
      }

      T homo(size_t a, size_t b)
        in { assert(n >= a+b-1); }
      do
      {
        return combi(a+b-1, b);
      }
    }
  }
}

auto io = IO!()();
import std.stdio;
struct IO(alias IN = stdin, alias OUT = stdout)
{
  import std.meta : allSatisfy;
  import core.stdc.stdlib : exit;

  void getV(T...)(ref T v)
  {
    foreach (ref w; v) get(w);
  }
  void getA(T)(size_t n, ref T v)
    if (hasAssignableElements!T)
  {
    v = new T(n);
    foreach (ref w; v) get(w);
  }
  void getC(T...)(size_t n, ref T v)
    if (allSatisfy!(hasAssignableElements, T))
  {
    foreach (ref w; v) w = new typeof(w)(n);
    foreach (i; 0..n) foreach (ref w; v) get(w[i]);
  }
  void getM(T)(size_t r, size_t c, ref T v)
    if (hasAssignableElements!T && hasAssignableElements!(ElementType!T))
  {
    v = new T(r);
    foreach (ref w; v) getA(c, w);
  }
  template getS(E...)
  {
    void getS(T)(size_t n, ref T v)
    {
      v = new T(n);
      foreach (ref w; v) foreach (e; E) mixin("get(w."~e~");");
    }
  }

  const struct PutConf
  {
    bool newline = true, flush, exit;
    string floatFormat = "%.10f", delimiter = " ";
  }

  void put(alias conf = "{}", T...)(T v)
  {
    mixin("const PutConf c = "~conf~"; putMain!c(v);");
  }
  void putB(alias conf = "{}", S, T)(bool c, S t, T f)
  {
    if (c) put!conf(t);
    else put!conf(f);
  }
  void putRaw(T...)(T v)
  {
    OUT.write(v);
    OUT.writeln;
  }

  private
  {
    dchar[] buf;
    auto sp = (new dchar[](0)).splitter;

    void nextLine()
    {
      IN.readln(buf);
      sp = buf.splitter;
    }
    void get(T)(ref T v)
    {
      if (sp.empty) nextLine();
      v = sp.front.to!T;
      sp.popFront();
    }

    void putMain(PutConf c, T...)(T v)
    {
      foreach (i, w; v) {
        putOne!c(w);
        if (i+1 < v.length) OUT.write(c.delimiter);
      }
      static if (c.newline) OUT.writeln;
      static if (c.flush) OUT.flush();
      static if (c.exit) exit(0);
    }
    void putOne(PutConf c, T)(T v)
    {
      static if (isInputRange!T && !isSomeString!T) putRange!c(v);
      else static if (isFloatingPoint!T) OUT.write(format(c.floatFormat, v));
      else static if (hasMember!(T, "fprint")) v.fprint(OUT);
      else OUT.write(v);
    }
    void putRange(PutConf c, T)(T v)
    {
      auto w = v;
      while (!w.empty) {
        putOne!c(w.front); w.popFront();
        if (!w.empty) OUT.write(c.delimiter);
      }
    }
  }
}