def rank(a,b,c,p):
  if p==0:
    return a
  elif p==1:
    return b
  elif p ==2:
    return c
  else:
    return 1

def sumrank(a,b,c,N,P):
  if N == 1:
    return rank(a[0],b[0],c[0],P)
  else:
    maxlastp = min(P,3)
    minlastp = max(0,P - 3*(N-1))
    result = []
    for lastp in range(minlastp,maxlastp +1):
      result.append(sumrank(a[0:N-1],b[0:N-1],c[0:N-1],N-1,P-lastp) + rank(a[N-1],b[N-1],c[N-1],lastp))
    return min(result)

def averagerank(a,b,c,N,P):
  return float(sumrank(a,b,c,N,P))/float(N)

input = raw_input()
N=int(input.split(' ')[0])
P =int(input.split(' ')[1])
a = []
b = []
c = []
for i in range(N):
  input = raw_input()
  a.append(int(input.split(' ')[0]))
  b.append(int(input.split(' ')[1]))
  c.append(int(input.split(' ')[2]))
print averagerank(a,b,c,N,P)