import std.algorithm, std.conv, std.range, std.stdio, std.string;

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

  int[][int][int] buf;
  foreach (_; m.iota) {
    auto rd2 = readln.split.to!(int[]), a = rd2[0] - 1, b = rd2[1] - 1, c = rd2[2];
    buf[c][a] ~= b;
    buf[c][b] ~= a;
  }

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

  auto ei = buf[di.front].keys.sort().uniq();
  foreach (d; di.drop(1)) {
    int[] fi;
    foreach (e; ei)
      if (e in buf[d]) fi ~= buf[d][e];
    ei = fi.sort().uniq();
  }

  writeln(ei.array.length);
  writeln(ei.map!"a + 1".map!(to!string).join(" "));
}