from math import comb
import numpy as np

def str2int(str):
    mm = int(str[:2])
    ss = int(str[3:])
    return 60 * mm + ss

n, l = map(int, input().split())
l *= 60
s = [0] * n
str_s = list(input().split())
for i in range(n): s[i] = str2int(str_s[i])

ssm = 0
for si in s: ssm += si
if ssm <= l: print(n)
else:
    dp = np.zeros((n + 1, n + 1, l + 1))
    for k in range(l + 1): dp[0][0][k] = 1

    for i in range(n):
        for j in range(n + 1):
            for k in range(l + 1):
                dp[i + 1][j][k] += dp[i][j][k]
                if j - 1 >= 0 and k - s[i] >= 0:
                    dp[i + 1][j][k] += dp[i][j - 1][k - s[i]]
    
    for i in range(n):
        for j in range(n + 1):
            for k in range(l + 1):
                dp[i][j][k] = dp[n][j][k]
                if j - 1 >= 0 and k - s[i] >= 0:
                    dp[i][j][k] -= dp[i][j - 1][k - s[i]]

    ans = 0.0
    for i in range(n):
        for j in range(n):
            if l - s[i] - 1 < 0:
                ans += dp[i][j][l - 1] * (j + 1) / n / comb(n - 1, j)
            else:
                ans += (dp[i][j][l - 1] - dp[i][j][l - s[i] - 1]) * (j + 1) / n / comb(n - 1, j)
    print(ans)