#include<iostream>
using namespace std;

int dp[1001][101];

int main()
{
	int n, m, k;

	int a[1001], b[1001], c[1001], d[1001];

	cin >> n >> m >> k;

	for (int i = 1; i <= m; i++)
	{
		cin >> a[i] >> b[i] >> c[i];
	}

	for (int i = 1; i <= k; i++)
	{
		cin >> d[i];
	}

	for (int i = 1; i <= k; i++)
	{
		for (int j = 1; j <= m; j++)
		{
			if (i > 1)
			{
				if (d[i] == c[j] && dp[i - 1][a[j]] == 1) 
				{
					dp[i][b[j]] = 1;
				}
				if (d[i] == c[j] && dp[i - 1][b[j]] == 1)
				{
					dp[i][a[j]] = 1;
				}
 			}
			else
			{
				if (d[i] == c[j])
				{
					dp[i][a[j]] = 1;
					dp[i][b[j]] = 1;
				}
			}
		}
	}

	int count = 0;
	for (int i = 1; i <= n; i++)
	{
		if (dp[k][i] == 1)
		{
			count++;
		}
	}

	cout << count << endl;

	for (int i = 1; i <= n; i++)
	{
		if (dp[k][i] == 1)
		{
			cout << i << " ";
		}
	}
	cout << endl;
}