from collections import defaultdict

def main():
    import sys
    input = sys.stdin.read().split()
    idx = 0
    N = int(input[idx]); idx += 1
    M = int(input[idx]); idx += 1
    K = int(input[idx]); idx += 1
    
    roads_dict = defaultdict(list)
    for _ in range(M):
        a = int(input[idx]); idx += 1
        b = int(input[idx]); idx += 1
        c = int(input[idx]); idx += 1
        roads_dict[c].append( (a, b) )
    
    d = list(map(int, input[idx:idx+K]))
    idx += K
    
    possible_prev = set(range(1, N+1))  # initially all towns are possible
    
    for cost in d:
        possible_curr = set()
        # Iterate through all roads with current cost
        for a, b in roads_dict.get(cost, []):
            if a in possible_prev:
                possible_curr.add(b)
            if b in possible_prev:
                possible_curr.add(a)
        possible_prev = possible_curr
    
    result = sorted(possible_prev)
    print(len(result))
    print(' '.join(map(str, result)))

if __name__ == '__main__':
    main()