#include <algorithm>
#include <iostream>
#include <cstdio>
#include <map>
#include <numeric>
#include <cmath>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <complex>
#include <string.h>
#include <unordered_set>
#include <unordered_map>
#include <bitset>
#include <iomanip>
#include <sys/time.h>
#include <random>
using namespace std;

#define endl '\n'
#define ALL(v) (v).begin(), (v).end()
#define RALL(v) (v).rbegin(), (v).rend()
#define UNIQ(v) (v).erase(unique((v).begin(), (v).end()), (v).end())

typedef long long ll;
typedef long double ld;
typedef pair<int, int> P;
typedef complex<double> comp;
typedef vector< vector<ld> > matrix;
struct pairhash {
public:
    template<typename T, typename U>
    size_t operator()(const pair<T, U> &x) const {
	size_t seed = hash<T>()(x.first);
	return hash<U>()(x.second) + 0x9e3779b9 + (seed<<6) + (seed>>2);
    }
};
const int inf = 1e9 + 9;
const ll mod = 1e9 + 7;
const double eps = 1e-8;
const double pi = acos(-1);

int n, l;
int s[55];

ll dp[55][60*60*55];
ll t[55][60*60*55];

double fact[55];
void calc_fact() {
    fact[0] = fact[1] = 1.0;
    for (int i = 2; i <= n; i++) fact[i] = fact[i-1] * i;
}

double solve() {
    calc_fact();
    l *= 60;
    int sum = 0;
    for (int i = 0; i < n; i++) sum += s[i];
    if (sum <= l) return n;

    dp[0][0] = 1;
    for (int i = 0; i < n; i++) {
        for (int j = n; j >= 1; j--) {
            for (int k = l; k >= s[i]; k--) {
                dp[j][k] += dp[j-1][k-s[i]];
            }
        }
    }

    double res = 0;
    for (int i = 0; i < n; i++) {
        memset(t, 0, sizeof(t));
        for (int j = 0; j < n; j++) {
            for (int k = 0; k < l; k++) {
                t[j][k] = dp[j][k];
                if (k>=s[i] && j>0) t[j][k] -= t[j-1][k-s[i]];
                res += t[j][k] * fact[j] * fact[n-1-j];
            }
        }
    }
    res /= fact[n];
    return res;
}

int convert(string t) {
    return 60 * (10 * (t[0]-'0') + t[1]-'0') + (10 * (t[3]-'0') + t[4]-'0');
}

void input() {
    cin >> n >> l;
    string t;
    for (int i = 0; i < n; i++) {
        cin >> t;
        s[i] = convert(t);
    }
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);

    input();
    cout << solve() << endl;
}