#define rep1( i, n )	for( int i = 1; i <= n; i++ )

#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 m;
int N;
int M;
int K;
int iCnt;

	cin >> N;
	cin >> M;
	cin >> K;
	rep1( i, M )
	{
		cin >> R[ i ].a;
		cin >> R[ i ].b;
		cin >> R[ i ].c;
	}

	rep1( m, K ) cin >> d[ m ];

	rep1( i, N ) bPre[ i ] = true;

	rep1( m, K )
	{
		rep1( i, N ) b[ i ] = false;

		rep1( j, M )
		{
			if( d[ m ] != R[ j ].c ) continue;

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

		rep1( i, N ) bPre[ i ] = b[ i ];
	}

	iCnt = 0;
	rep1( i, N )
	{
		if( b[ i ] ) iCnt++;
	}

	cout << iCnt << endl;
	rep1( i, N )
	{
		if( b[ i ] ) cout << i << " ";
	}

	cout << endl;
	return 0;
}