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

struct Root
{
	int a;
	int b;
	int c;
};

Root R[ 1010 ];
int d[ 1010 ];

bool bPre[ 110 ];
bool b[ 110 ];

int main()
{
int i;
int j;
int k;
int N;
int M;
int K;
int iCnt;

	cin >> N;
	cin >> M;
	cin >> K;
	for( i = 1; i <= M; i++ )
	{
		cin >> R[ i ].a;
		cin >> R[ i ].b;
		cin >> R[ i ].c;
	}

	for( i = 1; i <= K; i++ ) cin >> d[ i ];

	for( i = 1; i <= N; i++ ) bPre[ i ] = true;

	for( i = 1; i <= K; i++ )
	{
		for( k = 1; k <= N; k++ ) b[ k ] = false;

		for( j = 1; j <= M; j++ )
		{
			if( d[ i ] != R[ j ].c ) continue;

			if( bPre[ R[ j ].a ] ) b[ R[ j ].b ] = true;
			if( bPre[ R[ j ].b ] ) b[ R[ j ].a ] = true;
		}

		for( k = 1; k <= N; k++ ) bPre[ k ] = b[ k ];
	}

	iCnt = 0;
	for( k = 1; k <= N; k++ )
	{
		if( b[ k ] ) iCnt++;
	}

	cout << iCnt << endl;
	for( i = 1; i <= N; i++ )
	{
		if( b[ i ] ) cout << i << " ";
	}

	cout << endl;
	return 0;
}