import math
import copy
def conv(s):
 return int(s[:2])*60+int(s[3:])

N,L=map(int,raw_input().split())
S=map(conv, raw_input().split())
dp= [[0 for k in range(L*60+1+3600)] for i in range(N+1)] 
dp[0][0]=1

alllen=0
for i in range(N):
    s=S[i]
    alllen+=s
    for j in range(N,-1,-1):
        for k in range(L*60+3600,-1,-1):
            if dp[j][k]!=0:
                dp[j+1][min(L*60+3600,k+s)]+=dp[j][k]
        
if alllen <= L*60:
    print N
    exit()

tot=0

for s in S:
    dp2=copy.deepcopy(dp)
    for j in range(0,N+1):
        num = 0
        for k in range(L*60+3600+1):
            if k-s>=0 and j-1 >= 0:
                dp2[j][k] -= dp2[j-1][k-s]
            if k+s >= 60*L and k < 60*L:
                num+=dp2[j][k]
        #print s,"+",j,"elements: ",num
        if num>0:
            tot += (j+1)*num*math.factorial(j)*math.factorial(N-j-1)

print tot*1.0/math.factorial(N)