N, M, K = [int(x) for x in input().split()]
a = [0] * M
b = [0] * M
c = [0] * M
for i in range(M):
    a[i], b[i], c[i] = [int(x) for x in input().split()]
d = [int(x) for x in input().split()]

pos = [[False] * (N + 1) for _ in range(K + 1)]
for i in range(1, len(pos[0])):
    pos[0][i] = True

for kk in range(K):
    for mm in range(M):
        if c[mm] == d[kk]:
            if pos[kk][a[mm]]:
                pos[kk + 1][b[mm]] = True
            if pos[kk][b[mm]]:
                pos[kk + 1][a[mm]] = True

cnt = pos[K].count(True)
lis = []
for nn, ok in enumerate(pos[K]):
    if ok:
        lis += [str(nn)]
print(cnt)
print(' '.join(lis))