#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <string>
#include <map>
#include <bitset>
#include <vector>
#include <queue>


typedef long long ll;
#define fi first
#define se second
const ll mod = 1000000007;
//              123456789

using namespace std;

///////////////////////////////////////////////
//
//
///////////////////////////////////////////////

////////////////////////////////////////////////
////////////////////////////////////////////////

int N;
int M;
int K;
int cost;
int c[1123];
int s[1123];
int d[1123];
int a[1123];
int b[1123];
bool P[1123][112][112];
bool dp[1123][112];
int ans = 0;
int idx;
int OUT[112];

int main(){
	
	int i;
	int j;
	int flag = 0;
	
	cin>>N>>M>>K;
	
	for( i = 0; i < M; i++ ){
		scanf("%d %d %d", a+i, b+i, c+i);
		s[i] = c[i];
	}
	
	for( i = 0; i < K; i++ ){
		scanf("%d", d+i );
	}
	
	sort( s, s+M );
	
	int cnt = 0;
	
	for( i = 1; i < M; i++ ){
		if( s[i] == s[i-1] ){
			s[i-1] = mod;
			cnt++;
		}
	}
	
	sort( s, s+M );
	
	for( i = 0; i < M; i++ ){
		for( j = 0; j < M-cnt; j++ ){
			if( c[i] == s[j] ){
				c[i] = j+1;
			}
		}
	}
	
	for( i = 0; i < K; i++ ){
		for( j = 0; j < M-cnt; j++ ){
			if( d[i] == s[j] ){
				d[i] = j+1;
			}
		}
	}
	
	fill( P[0][0], P[1123][112], 0 );
	
	for( i = 0; i < M; i++ ){	
		P[c[i]][b[i]][a[i]] = 1;
		P[c[i]][a[i]][b[i]] = 1;
	}
	
	fill( dp[0], dp[1], 1 );
	fill( dp[1], dp[K+1], 0 );
	
	int o;
	
	for( i = 0; i < K; i++ ){
		for( j = 1; j <= N; j++ ){
			if( dp[i][j] ){
				for( o = 1; o <= N; o++ ){
					if( P[d[i]][j][o]){
						dp[i+1][o] = 1;
					}
				}
			}
		}
	}
	
	
	
	
	for( i = 1; i <= N; i++ ){
		OUT[ans] = i;
		if( dp[K][i] ) ans++;
	} 
	
	cout<<ans<<endl;
	
	for( i = 0; i < ans; i++ ){
		if( i ) printf(" ");
		printf("%d", OUT[i] );
	}
	
	puts("");
	
	return 0;
	
}