import sys

# sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = (1 << 63)-1
# md = 10**9+7
md = 998244353

from copy import deepcopy

n, l = LI()

fac = [1]
for i in range(1, n+1): fac.append(fac[-1]*i)
pp = [0]*n
for i in range(n): pp[i] = fac[i]*fac[n-1-i]/fac[-1]

l *= 60
ss = SI().split()
ss = [int(s[0:2])*60+int(s[3:5]) for s in ss]
tot = sum(ss)

if tot <= l:
    print(n)
    exit()

dp = [[0]*l for _ in range(n+1)]
dp[0][0] = 1

for si, s in enumerate(ss):
    for i in range(si+1, 0, -1):
        for j in range(s, l):
            dp[i][j] += dp[i-1][j-s]
# p2D(dp)

ans = 0
for s in ss:
    cdp = deepcopy(dp)
    for i in range(n):
        for j in range(l):
            if i and j >= s: cdp[i][j] -= cdp[i-1][j-s]
            ans += cdp[i][j]*pp[i]

print(f"{ans:.10f}")