class Calc0092
  def initialize(args)
    args = args.map { |l| l.chomp.split(/\s+/) }
    @n, @m, @k = args.shift.map(&:to_i)
    @roads = args.shift(@m).map { |l| l.map(&:to_i) }
    @ds = args.shift.map(&:to_i)
  end

  def run
    h = @roads.group_by { |r| r[2] }.map { |k, v|
      [k, v.flat_map { |w| [[w[0], w[1]], [w[1], w[0]]] }]
    }.to_h

    cands = h[@ds.shift].map(&:last).uniq
    @ds.each do |d|
      cands = h[d].select { |w| cands.include?(w.first) }.map(&:last).uniq
    end
    [cands.size, cands.sort.join(' ')].join("\n")
  end
end

puts Calc0092.new(STDIN.readlines).run if __FILE__ == $0