#include <bits/stdc++.h>
#define REP_(i, a_, b_, a, b, ...) \
  for (int i = (a), END_##i = (b); i < END_##i; ++i)
#define REP(i, ...) REP_(i, __VA_ARGS__, __VA_ARGS__, 0, __VA_ARGS__)
#define ALL(x) std::begin(x), std::end(x)
using Int = long long;
using Real = long double;

template<typename T, typename U>
inline bool chmax(T &a, U b) {
  return a < b and ((a = std::move(b)), true);
}
template<typename T, typename U>
inline bool chmin(T &a, U b) {
  return a > b and ((a = std::move(b)), true);
}
template<typename T>
inline int ssize(const T &a) {
  return (int) a.size();
}

template<class T>
inline std::ostream &print_one(const T &x, char endc) {
  if constexpr (std::is_same_v<T, bool>) {
    return std::cout << (x ? "Yes" : "No") << endc;
  } else {
    return std::cout << x << endc;
  }
}
template<class T>
inline std::ostream &print(const T &x) { return print_one(x, '\n'); }
template<typename T, typename... Ts>
std::ostream &print(const T &head, Ts... tail) {
  return print_one(head, ' '), print(tail...);
}
inline std::ostream &print() { return std::cout << '\n'; }

template<typename Container>
std::ostream &print_seq(const Container &a, std::string_view sep = " ",
                        std::string_view ends = "\n",
                        std::ostream &os = std::cout) {
  auto b = std::begin(a), e = std::end(a);
  for (auto it = std::begin(a); it != e; ++it) {
    if (it != b) os << sep;
    os << *it;
  }
  return os << ends;
}

template<typename T, typename = void>
struct is_iterable : std::false_type {};
template<typename T>
struct is_iterable<T, std::void_t<decltype(std::begin(std::declval<T>())),
                                  decltype(std::end(std::declval<T>()))>>
    : std::true_type {
};

template<typename T, typename = std::enable_if_t<
    is_iterable<T>::value && !std::is_same<T, std::string>::value>>
std::ostream &operator<<(std::ostream &os, const T &a) {
  return print_seq(a, ", ", "", (os << "{")) << "}";
}

struct CastInput {
  template<typename T>
  operator T() const {
    T x;
    std::cin >> x;
    return x;
  }
  struct Sized {
    std::size_t n;
    template<typename T>
    operator T() const {
      T x(n);
      for (auto &e: x) std::cin >> e;
      return x;
    }
  };
  Sized operator()(std::size_t n) const { return {n}; }
} const in;

inline void check(bool cond, const char *message = "!ERROR!") {
  if (not cond) throw std::runtime_error(message);
}

#ifdef MY_DEBUG
#include "debug_dump.hpp"
#else
#define DUMP(...)
#define cerr if(false)std::cerr
#endif

using namespace std;

template<typename T, int DMAX>
struct NaiveMult {
  using value_type = T;
  static constexpr int dmax() { return DMAX; }

  static std::vector<T> multiply(const std::vector<T> &x,
                                 const std::vector<T> &y) {
    const int n = std::min<int>(x.size() + y.size() - 1, DMAX + 1);
    const int mi = std::min<int>(x.size(), n);
    std::vector<T> res(n);
    for (int i = 0; i < mi; ++i) {
      for (int j = 0; j < int(y.size()); ++j) {
        if (i + j >= n) break;
        res[i + j] += x[i] * y[j];
      }
    }
    return res;
  }

  static std::vector<T> invert(const std::vector<T> &x) {
    std::vector<T> res(DMAX + 1);
    res[0] = x[0].inv();
    for (int i = 1; i <= DMAX; ++i) {
      T s = 0;
      const int mj = std::min<int>(i + 1, x.size());
      for (int j = 1; j < mj; ++j) {
        s += x[j] * res[i - j];
      }
      res[i] = -res[0] * s;
    }
    return res;
  }
};

// Formal Power Series (dense format).
template<typename Mult>
struct DenseFPS {
  using T = typename Mult::value_type;
  static constexpr int dmax() { return Mult::dmax(); }

  // Coefficients of terms from x^0 to x^DMAX.
  std::vector<T> coeff_;

  DenseFPS() : coeff_(1, 0) {}  // = 0 * x^0

  explicit DenseFPS(std::vector<T> c) : coeff_(std::move(c)) {
    while (size() > dmax() + 1) coeff_.pop_back();
    assert(size() > 0);
  }
  DenseFPS(std::initializer_list<T> init) : coeff_(init.begin(), init.end()) {
    while (size() > dmax() + 1) coeff_.pop_back();
    assert(size() > 0);
  }

  DenseFPS(const DenseFPS &other) : coeff_(other.coeff_) {}
  DenseFPS(DenseFPS &&other) : coeff_(std::move(other.coeff_)) {}
  DenseFPS &operator=(const DenseFPS &other) {
    coeff_ = other.coeff_;
    return *this;
  }
  DenseFPS &operator=(DenseFPS &&other) {
    coeff_ = std::move(other.coeff_);
    return *this;
  }

  // size <= dmax + 1
  inline int size() const { return static_cast<int>(coeff_.size()); }

  // Returns the coefficient of x^k.
  inline T operator[](int k) const { return (k >= size()) ? 0 : coeff_[k]; }

  DenseFPS &operator+=(const T &scalar) {
    coeff_[0] += scalar;
    return *this;
  }
  friend DenseFPS operator+(const DenseFPS &f, const T &scalar) {
    return DenseFPS(f) += scalar;
  }
  DenseFPS &operator+=(const DenseFPS &other) {
    if (size() < other.size()) coeff_.resize(other.size());
    for (int i = 0; i < other.size(); ++i) coeff_[i] += other[i];
    return *this;
  }
  friend DenseFPS operator+(const DenseFPS &f, const DenseFPS &g) {
    return DenseFPS(f) += g;
  }

  DenseFPS &operator-=(const DenseFPS &other) {
    if (size() < other.size()) coeff_.resize(other.size());
    for (int i = 0; i < other.size(); ++i) coeff_[i] -= other[i];
    return *this;
  }
  friend DenseFPS operator-(const DenseFPS &f, const DenseFPS &g) {
    return DenseFPS(f) -= g;
  }

  DenseFPS operator-() const { return *this * -1; }

  DenseFPS &operator*=(const T &scalar) {
    for (auto &x: coeff_) x *= scalar;
    return *this;
  }
  friend DenseFPS operator*(const DenseFPS &f, const T &scalar) {
    return DenseFPS(f) *= scalar;
  }
  friend DenseFPS operator*(const T &scalar, const DenseFPS &g) {
    return DenseFPS{scalar} *= g;
  }
  DenseFPS &operator*=(const DenseFPS &other) {
    return *this =
               DenseFPS(Mult::multiply(std::move(this->coeff_), other.coeff_));
  }
  friend DenseFPS operator*(const DenseFPS &f, const DenseFPS &g) {
    return DenseFPS(Mult::multiply(f.coeff_, g.coeff_));
  }

  DenseFPS &operator/=(const T &scalar) {
    for (auto &x: coeff_) x /= scalar;
    return *this;
  }
  friend DenseFPS operator/(const DenseFPS &f, const T &scalar) {
    return DenseFPS(f) /= scalar;
  }
  friend DenseFPS operator/(const T &scalar, const DenseFPS &g) {
    return DenseFPS{scalar} /= g;
  }
  DenseFPS &operator/=(const DenseFPS &other) {
    return *this *= DenseFPS(Mult::invert(other.coeff_));
  }
  friend DenseFPS operator/(const DenseFPS &f, const DenseFPS &g) {
    return f * DenseFPS(Mult::invert(g.coeff_));
  }

  DenseFPS pow(Int t) const {
    assert(t >= 0);
    DenseFPS res = {1}, base = *this;
    while (t) {
      if (t & 1) res *= base;
      base *= base;
      t >>= 1;
    }
    return res;
  }

  // Multiplies by (1 + c * x^k).
  void multiply2_inplace(int k, int c) {
    assert(k > 0);
    if (size() <= dmax()) {
      coeff_.resize(min(size() + k, dmax() + 1), 0);
    }
    for (int i = size() - 1; i >= k; --i) {
      coeff_[i] += coeff_[i - k] * c;
    }
  }
  // Multiplies by (1 + c * x^k).
  DenseFPS multiply2(int k, int c) const {
    DenseFPS res = *this;
    res.multiply2_inplace(k, c);
    return res;
  }

  // Divides by (1 + c * x^k).
  void divide2_inplace(int k, int c) {
    assert(k > 0);
    for (int i = k; i < size(); ++i) {
      coeff_[i] -= coeff_[i - k] * c;
    }
  }
  // Divides by (1 + c * x^k).
  DenseFPS divide2(int k, int c) const {
    DenseFPS res = *this;
    res.divide2_inplace(k, c);
    return res;
  }

  // Multiplies by x^k.
  void shift_inplace(int k) {
    if (k > 0) {
      if (size() <= dmax()) {
        coeff_.resize(min(size() + k, dmax() + 1), 0);
      }
      for (int i = size() - 1; i >= k; --i) {
        coeff_[i] = coeff_[i - k];
      }
      for (int i = k - 1; i >= 0; --i) {
        coeff_[i] = 0;
      }
    } else if (k < 0) {
      k *= -1;
      for (int i = k; i < size(); ++i) {
        coeff_[i - k] = coeff_[i];
      }
      for (int i = size() - k; i < size(); ++i) {
        // If coefficients of degrees higher than dmax() were truncated
        // beforehand, you lose the information. Ensure dmax() is big enough.
        coeff_[i] = 0;
      }
    }
  }
  // Multiplies by x^k.
  DenseFPS shift(int k) const {
    DenseFPS res = *this;
    res.shift_inplace(k);
    return res;
  }

  T eval(const T &a) const {
    T res = 0, x = 1;
    for (auto c: coeff_) {
      res += c * x;
      x *= a;
    }
    return res;
  }
};

// Formal Power Series (sparse format).
template<typename T>
struct SparseFPS {
  int size_;
  std::vector<int> degree_;
  std::vector<T> coeff_;

  SparseFPS() : size_(0) {}

  explicit SparseFPS(std::vector<std::pair<int, T>> terms)
      : size_(terms.size()), degree_(size_), coeff_(size_) {
    // Sort by degree.
    std::sort(terms.begin(), terms.end(),
              [](const auto &x, const auto &y) { return x.first < y.first; });
    for (int i = 0; i < size_; ++i) {
      auto[d, c] = terms[i];
      assert(d >= 0);
      degree_[i] = d;
      coeff_[i] = c;
    }
  }

  SparseFPS(std::initializer_list<std::pair<int, T>> terms)
      : SparseFPS(std::vector<std::pair<int, T>>(terms.begin(), terms.end())) {}

  inline int size() const { return size_; }
  inline const T &coeff(int i) const { return coeff_[i]; }
  inline int degree(int i) const { return degree_[i]; }
  int max_degree() const { return (size_ == 0) ? 0 : degree_.back(); }

  void emplace_back(int d, T c) {
    assert(d >= 0);
    if (not degree_.empty()) {
      assert(d > degree_.back());
    }
    degree_.push_back(std::move(d));
    coeff_.push_back(std::move(c));
    ++size_;
  }

  // Returns the coefficient of x^d.
  T operator[](int d) const {
    auto it = std::lower_bound(degree_.begin(), degree_.end(), d);
    if (it == degree_.end() or *it != d) return (T) (0);
    int j = std::distance(degree_.begin(), it);
    return coeff_[j];
  }

  SparseFPS &operator+=(const T &scalar) {
    for (auto &x: coeff_) x += scalar;
    return *this;
  }
  friend SparseFPS operator+(const SparseFPS &f, const T &scalar) {
    SparseFPS res = f;
    res += scalar;
    return res;
  }
  SparseFPS &operator+=(const SparseFPS &other) {
    *this = this->add(other);
    return *this;
  }
  friend SparseFPS operator+(const SparseFPS &f, const SparseFPS &g) {
    return f.add(g);
  }

  SparseFPS &operator*=(const T &scalar) {
    for (auto &x: coeff_) x *= scalar;
    return *this;
  }
  friend SparseFPS operator*(const SparseFPS &f, const T &scalar) {
    SparseFPS res = f;
    res *= scalar;
    return res;
  }

  SparseFPS &operator-=(const SparseFPS &other) {
    *this = this->add(other * -1);
    return *this;
  }
  friend SparseFPS operator-(const SparseFPS &f, const SparseFPS &g) {
    return f.add(g * -1);
  }

 private:
  SparseFPS add(const SparseFPS &other) const {
    SparseFPS res;
    int j = 0;  // two pointers (i, j)
    for (int i = 0; i < size(); ++i) {
      const int deg = this->degree(i);
      for (; j < other.size() and other.degree(j) < deg; ++j) {
        res.emplace_back(other.degree(j), other.coeff(j));
      }
      T c = this->coeff(i);
      if (j < other.size() and other.degree(j) == deg) {
        c += other.coeff(j);
        ++j;
      }
      if (c != 0) {
        res.emplace_back(deg, c);
      }
    }
    for (; j < other.size(); ++j) {
      res.emplace_back(other.degree(j), other.coeff(j));
    }
    return res;
  }
};

// Polynomial addition (dense + sparse).
template<typename FPS, typename T = typename FPS::T>
FPS &operator+=(FPS &f, const SparseFPS<T> &g) {
  for (int i = 0; i < g.size(); ++i) {
    if (g.degree(i) > FPS::dmax()) break;  // ignore
    f.coeff_[g.degree(i)] += g.coeff(i);
  }
  return f;
}
template<typename FPS, typename T = typename FPS::T>
FPS operator+(const FPS &f, const SparseFPS<T> &g) {
  auto res = f;
  res += g;
  return res;
}
template<typename FPS, typename T = typename FPS::T>
FPS operator+(const SparseFPS<T> &f, const FPS &g) {
  return g + f;  // commutative
}

// Polynomial multiplication (dense * sparse).
template<typename FPS, typename T = typename FPS::T>
FPS &operator*=(FPS &f, const SparseFPS<T> &g) {
  if (g.size() == 0) {
    return f *= 0;
  }
  const int gd_max = g.degree(g.size() - 1);
  const int fd_max = f.size() - 1;
  const int n = std::min(fd_max + gd_max, FPS::dmax()) + 1;
  if (f.size() < n) f.coeff_.resize(n);

  T c0 = 0;
  int j0 = 0;
  if (g.degree(0) == 0) {
    c0 = g.coeff(0);
    j0 = 1;
  }

  for (int fd = n - 1; fd >= 0; --fd) {
    f.coeff_[fd] *= c0;
    for (int j = j0; j < g.size(); ++j) {
      int gd = g.degree(j);
      if (gd > fd) break;
      f.coeff_[fd] += f[fd - gd] * g.coeff(j);
    }
  }
  return f;
}
template<typename FPS, typename T = typename FPS::T>
FPS operator*(const FPS &f, const SparseFPS<T> &g) {
  auto res = f;
  res *= g;
  return res;
}
template<typename FPS, typename T = typename FPS::T>
FPS operator*(const SparseFPS<T> &f, const FPS &g) {
  return g * f;  // commutative
}

// Polynomial division (dense / sparse).
template<typename FPS, typename T = typename FPS::T>
FPS &operator/=(FPS &f, const SparseFPS<T> &g) {
  assert(g.size() > 0 and g.degree(0) == 0 and g.coeff(0) != 0);
  const auto ic0 = T(1) / g.coeff(0);
  for (int fd = 0; fd < f.size(); ++fd) {
    for (int j = 1; j < g.size(); ++j) {
      int gd = g.degree(j);
      if (fd < gd) break;
      f.coeff_[fd] -= f.coeff_[fd - gd] * g.coeff(j);
    }
    f.coeff_[fd] *= ic0;
  }
  return f;
}
template<typename FPS, typename T = typename FPS::T>
FPS operator/(const FPS &f, const SparseFPS<T> &g) {
  FPS res = f;
  res /= g;
  return res;
}

constexpr int DMAX = 300 * 60 + 5;
using DF = DenseFPS<NaiveMult<Real, DMAX>>;
using SF = SparseFPS<Real>;

auto solve() -> Real {
  int n = in, L = in;
  L *= 60;
  DUMP(L);
  vector<int> S(n);
  DF f = {1.0};
  Int ssum = 0;
  REP(i, n) {
    int smin, ssec;
    scanf("%d:%d", &smin, &ssec);
    DUMP(i, smin, ssec);
    S[i] = 60 * smin + ssec;
    ssum += S[i];
    f *= SF{{0, 0.5}, {S[i], 0.5}};
    //DUMP(f.coeff_);
  }
  if (L >= ssum) {
    return n;
  }
  DUMP(S);
  Real ans = 0;
  REP(i, n) {
    DF g = {1.0};
    REP(j, n) {
      if (j == i) continue;
      g *= SF{{0, 0.5}, {S[j], 0.5}};
    }
    g.divide2_inplace(1, -1);
    ans += min<Real>(g[L - 1], 1);
  }
  return ans;
}

int main() {
//  ios_base::sync_with_stdio(false), cin.tie(nullptr);
  cout << std::fixed << std::setprecision(18);
  const int T = 1;//in;
  REP(t, T) {
    auto ans = solve();
    print(ans);
  }
}