import sys
input = lambda : sys.stdin.readline().rstrip()

sys.setrecursionlimit(2*10**5+10)
write = lambda x: sys.stdout.write(x+"\n")
debug = lambda x: sys.stderr.write(x+"\n")
writef = lambda x: print("{:.12f}".format(x))

def add(dp,v):
    """dp[i] : 和がiの通り数
    vを好きなだけ使えるときの通り数に更新
    """
    dp = dp
    for i in range(v,m+1):
        dp[i] += dp[i-v]
        if dp[i]>M:
            dp[i] -= M
    return dp
def sub(dp,v):
    """vを追加する前の通り数に戻す
    """
    for i in range(v,m+1)[::-1]:
        dp[i] -= dp[i-v]
        dp[i] %= M
    return dp

n,l = list(map(int, input().split()))
def f(v):
    m,s = map(int, v.split(":"))
    return 60*m + s
s = list(map(f, input().split()))
l *= 60
l -= 1
g = [1.0]
for i in range(1,51):
    g.append(g[-1]*i)
# if sum(s)<l:
if 0:
    ans = n
else:
    dp = [[0]*(l+1) for _ in range(n+1)] # i個使って和がj
    dp[0][0] = 1
    for i in range(n):
        v = s[i]
        for j in range(i+1)[::-1]:
            for k in range(l)[::-1]:
                val = dp[j][k]
                if val==0 or k+v>l:
                    continue
                dp[j+1][k+v] += val
    dp0 = [item[:] for item in dp]
    ans = 0
    for i in range(n):
        v = s[i]
        dp = [item[:] for item in dp0]
        for j in range(n):
            for k in range(l):
                val = dp[j][k]
                if val==0 or k+v>l:
                    continue
                dp[j+1][k+v] -= val
        res = 0
        for j in range(n):
            res += sum(dp[j]) * (g[j] * g[n-1-j] / g[n])
        ans += res
print(ans)
#     from pprint import pprint
#     print(dp)