def g;gets.split.map(&:to_i)end
n,m=g
l=Hash.new{|h,k|h[k]=Hash.new{[]}}
m.times{
  a,b,c=g
  l[c][a]+=[b]
  l[c][b]+=[a]
}
now=*1..n
g.each{|c|now=l[c].values_at(*now).flatten.uniq}
puts now.size,now.sort*" "