#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
#define rep(i, n) REP(i, 0, n)
#define REP(i, s, e) for (ll i = (s); i < (ll)(e); i++)
#define repr(i, n) REPR(i, n, 0)
#define REPR(i, s, e) for (ll i = (ll)(s - 1); i >= (ll)(e); i--)
#define all(r) r.begin(), r.end()
#define rall(r) r.rbegin(), r.rend()

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;

template <typename T, typename U>
bool chmax(T& a, const U& b) {
    if (a >= b) return false;
    a = b;
    return true;
}
template <typename T, typename U>
bool chmin(T& a, const U& b) {
    if (a <= b) return false;
    a = b;
    return true;
}

void yes_no(bool f, string yes = "Yes", string no = "No") {
    cout << (f ? yes : no) << "\n";
}

void solve() {
    int n, m;
    cin >> n >> m;
    m *= 60;
    vector<int> a(n);
    rep(i, n) {
        int x, y;
        char c;
        cin >> x >> c >> y;
        a[i] = x * 60 + y;
    }
    ll sum = accumulate(all(a), 0);
    if (sum <= m) {
        cout << n << '\n';
        return;
    }
    using D = long double;
    vector<D> f(n + 10);
    f[0] = f[1] = 1;
    REP(i, 2, n + 10)
    f[i] = f[i - 1] * i;
    const int ma = 2.5e4;
    vector<vector<ll>> dp(ma + 1, vector<ll>(n + 1));
    dp[0][0] = 1;
    rep(i, n) repr(x, i + 1) rep(y, ma) {
        dp[min(ma, (int)y + a[i])][x + 1] += dp[y][x];
    }
    vector ep(ma + 1, vector(n + 1, 0LL));
    D ans = 0;
    rep(i, n) {
        rep(x, n + 1) {
            rep(y, m + a[i]) {
                ep[y][x] = dp[y][x];
                if (y >= a[i] && x > 0) ep[y][x] -= ep[y - a[i]][x - 1];
                if (x < n && y < m) ans += ep[y][x] * f[x] * f[n - x - 1];
            }
        }
    }
    ans /= f[n];
    cout << fixed << setprecision(15);
    cout << ans << "\n";
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int t = 1;
    // multi-testcase
    // cin >> t;
    rep(ti, t) solve();
    return 0;
}