#include "bits/stdc++.h"
using namespace std;


int getnum(char c){
	return c - '0';
}

double dp[51][36002];
double predp[51][36002];
double functional[51];
int S[51];

int main() {
	int N, L;
	cin >> N >> L;
	L *= 60;
	double ans = 0;
	int sum = 0;
	for (int i = 0; i < N; i++)
	{
		string temp;
		cin >> temp;
		int time = getnum(temp[0]) * 600 + getnum(temp[1]) * 60 + getnum(temp[3]) * 10 + getnum(temp[4]);
		if (time > L) time = L;
		S[i] = time;
		sum += time;
	}

	if (L >= sum){
		cout << N << endl; return 0;
	}
	
	dp[0][0] = 1;
	for (int i = 0; i < N; i++)
	{
		for (int j = i; j >= 0; j--)
		{
			for (int k = 0; S[i] + k <= L * 2; k++)
			{
				if (!dp[j][k]) continue;
				dp[j + 1][S[i] + k] += dp[j][k];
			}
		}
	}

	functional[0] = 1;
	for (int i = 1; i < 51; i++)
	{
		functional[i] = functional[i - 1] * i;
	}

	double sump = 0;
	for (int i = 0; i < N; i++)
	{
		for (int j = 0; j < N; j++)
		{
			for (int k = 0; k < L; k++)
			{
				predp[j][k] = dp[j][k];
				if (j - 1 >= 0 && k - S[i] >= 0){
					predp[j][k] -= predp[j - 1][k - S[i]];
				}
				sump += predp[j][k] * functional[N - j - 1] * functional[j];
			}
		}
	}
	sump /= functional[N];
	ans += sump;
	printf("%.14f", ans);
	cin >> ans;
}