N, M, K = map(int, raw_input().strip().split())
abcs = [list(map(int, raw_input().strip().split())) for i in range(M)]
ds = map(int, raw_input().strip().split())
D = [[set() for j in range(N+1)] for i in range(N+1)]
for abc in abcs:
    a, b, c = abc
    D[a][b].add(c)
    D[b][a].add(c)


def dfs(s, lst):
    if not lst:
        return [s]
    return [x
            for t in range(N+1) if lst[0] in D[s][t]
            for x in dfs(t, lst[1:])]

ss = set(j for i in range(N+1) for j in range(N+1) if ds[0] in D[i][j])
ans = sorted(set(z for s in ss for z in dfs(s, ds[1:])))
L = len(ans)
print(L)
if L == 0:
    print(ans[0])
else:
    print(' '.join(map(str, ans)))