#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <sstream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <numeric>
#include <cctype>
#include <tuple>
#include <array>
#include <climits>
#include <bitset>
#include <cassert>

#ifdef _MSC_VER
#include <agents.h>
#endif

#define FOR(i, a, b) for(int i = (a); i < (int)(b); ++i)
#define rep(i, n) FOR(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define REV(v) v.rbegin(), v.rend()
#define MEMSET(v, s) memset(v, s, sizeof(v))
#define UNIQUE(v) (v).erase(unique(ALL(v)), (v).end())
#define MP make_pair
#define MT make_tuple

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> P;

ll dp[55][22000];
ll dp2[55][22000];
ll ans[55][22000];

ld fact[55];

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout.setf(ios::fixed);
	cout.precision(20);

	fact[0] = 1;
	for (int i = 1; i < 55; ++i) fact[i] = fact[i - 1] * i;

	int n, L;
	cin >> n >> L;
	L *= 60;
	vector<int> s(n);
	rep(i, n){
		int a, b;
		char c;
		cin >> a >> c >> b;
		s[i] = a * 60 + b;
	}

	int MX = L + 3600;
	dp[0][0] = 1;
	for (int i = 0; i < n; ++i){
		for (int j = i; j >= 0; --j){
			rep(k, MX){
				dp[j + 1][min(k + s[i], MX)] += dp[j][k];
			}
		}
	}

	ld ans = 0;
	for (int i = 0; i < n; ++i){
		MEMSET(dp2, 0);
		dp2[0][0] = 1;
		for (int j = 1; j <= n; ++j){
			for (int k = 0; k < L + s[i]; ++k){
				dp2[j][k] = dp[j][k];
				if (k - s[i] >= 0) dp2[j][k] -= dp2[j - 1][k - s[i]];
			}
		}

		rep(i, n){
			ld tmp = 0;
			rep(j, L){
				tmp += dp2[i][j];
			}
			ans += tmp*fact[i]*fact[n - 1 - i];
		}
	}

	cout << ans / fact[n] << endl;
}