#include "bits/stdc++.h"
using namespace std;


bool now[1000];
bool nex[1000];

int main(){
	int N, M, K;
	cin >> N >> M >> K;
	vector<int> a(M), b(M), c(M);
	for (int i = 0; i < M; i++)
	{
		cin >> a[i] >> b[i] >> c[i];
		a[i]--; b[i]--;
	}
	vector<int> d(K);
	for (int i = 0; i < K; i++)
	{
		cin >> d[i];
	}
	for (int i = 0; i < N; i++)
	{
		now[i] = true;
		nex[i] = false;
	}

	for (int i = 0; i < K; i++)
	{
		for (int j = 0; j < M; j++)
		{
			if (c[j] != d[i]) continue;
			nex[a[i]] |= now[b[i]];
			nex[b[i]] |= now[a[i]];
		}
		for (int j = 0; j < N; j++)
		{
			now[j] = nex[j];
			nex[j] = false;
		}
	}

	int count = 0;
	for (int i = 0; i < N; i++)
	{
		if (now[i]){
			count++;
		}
	}
	cout << count << endl;

	for (int i = 0; i < N; i++)
	{
		if (now[i]){
			if (--count) cout << (i + 1) << " "; 
			else cout << (i + 1) << endl;
		}
	}
}