def g;gets.split.map(&:to_i)end
n,m=g
l=Hash.new{[]}
m.times{
  *a,c=g
  l[c]+=[a]
}
now=*1..n
g.each{|c|now=l[c].flat_map{|a|a.select{|i|now.index(*(a-[i]))}}}
puts now.size,now*" "