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

int dp[30010][60] = {};
int dp2[30010][60] = {};

int main() {
    int N, L, S[60];
    cin >> N >> L;
    L *= 60;
    for (int i = 0; i < N; i++) {
        string s;
        cin >> s;
        for (auto& c : s)
            c -= '0';
        S[i] = (s[0] * 10 + s[1]) * 60 + (s[3] * 10 + s[4]);
    }

    dp[0][0] = 1;
    for (int i = 0; i < N; i++) {
        for (int x = 25000; x >= 0; x--) {
            for (int j = 0; j < N; j++) {
                dp[x + S[i]][j + 1] += dp[x][j];
            }
        }
    }

    double fact[60];
    fact[0] = 1;
    for (int i = 1; i <= N; i++) {
        fact[i] = fact[i - 1] * i;
    }

    double ans = 0;
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < N; j++) {
            for (int x = 0; x < L + S[i]; x++) {
                dp2[x][j] = dp[x][j];
                if (j > 0 && x >= S[i])
                    dp2[x][j] -= dp2[x - S[i]][j - 1];
                if (x < L)
                    ans += dp2[x][j] * fact[j] * fact[N - j - 1];
            }
        }
    }

    ans /= fact[N];
    cout << fixed << setprecision(10);
    cout << ans << endl;
}