import std.algorithm, std.array, std.container, std.range;
import std.string, std.conv;
import std.math, std.bigint, std.bitmanip, std.random;
import std.stdio, std.typecons;

alias Tuple!(int, "n1", int, "n2") side;

void main()
{
  auto rd1 = readln.split.map!(to!int);
  auto n = rd1[0], m = rd1[1], k = rd1[2];

  side[][int] si;
  foreach (_; 0..m) {
    auto rd2 = readln.split.map!(to!int);
    si[rd2[2]] ~= side(rd2[0] - 1, rd2[1] - 1);
  }

  auto di = readln.split.map!(to!int);

  auto cands = BitArray([]);
  cands.length = n;

  foreach (s; si[di[0]]) {
    cands[s.n1] = true;
    cands[s.n2] = true;
  }

  foreach (i; 1..k) {
    auto next = BitArray([]);
    next.length = n;
    foreach (s; si[di[i]]) {
      if (cands[s.n1])
        next[s.n2] = true;
      if (cands[s.n2])
        next[s.n1] = true;
    }
    cands = next;
  }

  auto r = cands.bitsSet.array;
  writeln(r.length);
  writeln(r.map!(x => x + 1).map!(to!string).join(' '));
}