$memo={}
def dfs(v,d,r)
	return 0 if d==v.size
	$memo[[d,r]]||=lambda{
		ret=Float::INFINITY
		(0..[r,3].min).each{|i|
			z=v[d][i]||1
			ret=[ret,dfs(v,d+1,r-i)+z].min
		}
		ret
	}.()
end
n,k=gets.split.map(&:to_i)
v=$<.map{|e|e.split.map(&:to_i)}
p dfs(v,0,k)/n.to_f