import std.conv, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.container, std.math, std.range, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) throw new EOFException; tokens = readln.split; } auto token = tokens[0]; tokens.popFront; return token; }
int readInt() { return readToken().to!int; }
long readLong() { return readToken().to!long; }
real readReal() { return readToken().to!real; }

void chmin(T)(ref T t, in T f) { if (t > f) t = f; }
void chmax(T)(ref T t, in T f) { if (t < f) t = f; }

int binarySearch(T)(in T[] as, in bool delegate(T) test) { int low = -1, upp = cast(int)(as.length); for (; low + 1 < upp; ) { int mid = (low + upp) >> 1; (test(as[mid]) ? low : upp) = mid; } return upp; }
int lowerBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a < val)); }
int upperBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a <= val)); }


int N, M, K;
int[] A, B, C;
int[] D;

void main() {
  try {
    for (; ; ) {
      N = readInt();
      M = readInt();
      K = readInt();
      A = new int[M];
      B = new int[M];
      C = new int[M];
      foreach (i; 0 .. M) {
        A[i] = readInt() - 1;
        B[i] = readInt() - 1;
        C[i] = readInt();
      }
      D = new int[K];
      foreach (k; 0 .. K) {
        D[k] = readInt();
      }
      
      auto graph = new int[][int][N];
      foreach (i; 0 .. M) {
        graph[A[i]][C[i]] ~= B[i];
        graph[B[i]][C[i]] ~= A[i];
      }
      
      auto dp = new bool[][](K + 1, N);
      dp[0][] = true;
      foreach (k; 0 .. K) {
        foreach (u; 0 .. N) {
          if (dp[k][u]) {
            foreach (v; graph[u].get(D[k], [])) {
              dp[k + 1][v] = true;
            }
          }
        }
      }
      
      int[] ans;
      foreach (u; 0 .. N) {
        if (dp[K][u]) {
          ans ~= u;
        }
      }
      writeln(ans.length);
      writeln(ans.map!(u => u + 1).to!string.replaceAll(regex(`[\[\],]`), ""));
    }
  } catch (EOFException e) {
  }
}