import sys
if sys.platform =='ios':
	import clipboard
	a=clipboard.get()
	a = a.split('\n')
	text = '\n'.join(a)
	with open('input_file.txt','w') as f:
		f.write(text)
	sys.stdin = open('input_file.txt')
sys.setrecursionlimit(410000000)
stdin = sys.stdin 
ni = lambda: int(ns())
ni_1 = lambda: int(ns())-1
na = lambda: list(map(int, stdin.readline().split()))
ns = lambda: stdin.readline().strip()
nm = lambda: map(int,input().split())
na_1 = lambda: list(map(lambda x:int(x)*(-1), stdin.readline().split()))
na_2 = lambda: list(map(lambda x:int(x)-1, stdin.readline().split()))

N,P = nm()
ABC = []
for i in range(N):
	ABC.append(na()+[1])


INF = 10**10	
dp = [[INF]*5001*3 for i in range(2)]
dp[0][0] = 0
for i in range(N):
	for j in range(P+1):
		for k in range(4):
			if j+k <= P:
				dp[1][j+k] = min(dp[0][j]+ABC[i][k],dp[1][j+k])
	for j in range(P+1):
		dp[0][j] = dp[1][j]
		dp[1][j] = INF
		
print(dp[0][P]/N)