def sol c, d, list
    if d.empty?
        return c
    end
    x = d.shift
    ans = []
    c.each{|s|
        list[s][0].each_with_index{|v,i|
            if v == x
                ans.push(list[s][1][i])
            end
            }
        }
    return sol(ans.uniq, d, list)
end
    
n,m,k = gets.split.map(&:to_i)
fee = Hash.new([])
list = Array.new(n)
n.times{|i|
    list[i] = Array.new(2)
    list[i][0] = []
    list[i][1] = []
    }
m.times{
    a,b,c = gets.split.map(&:to_i)
    fee[c] = fee[c] + [a - 1,b - 1]
    list[a - 1][0].push(c)
    list[a - 1][1].push(b - 1)
    list[b - 1][0].push(c)
    list[b - 1][1].push(a - 1)
    }
d = gets.split.map(&:to_i)
x = d.shift
ans = sol(fee[x].uniq, d, list).map{|i|i + 1}.sort
p ans.size
puts ans.join(' ')