function main(input) {
  const [n, m, k] = getIntegers(input);
  const mList = twoDimensionalArray(n, n, []);
  for(let i=0; i<m; i++) {
    const [p1, p2, cost] = getIntegers(input);
    mList[p1-1][p2-1].push(cost);
    mList[p2-1][p1-1].push(cost);
  }
  const kList = getIntegers(input);
  
  let ansSet = new Set();
  for(let i=0; i<n; i++) {
    for(let j=0; j<n; j++) {
      if(mList[i][j].indexOf(kList[0]) >= 0) {
        ansSet.add(j+1);
      }
    }
  }
  for(let i=1; i<k; i++) {
    const nextK = kList[i];
    let nextAnsSet = new Set();
    ansSet.forEach(function(from) {
      for(let to=0; to<n; to++) {
        if(mList[from-1][to].indexOf(nextK) >= 0) {
          nextAnsSet.add(to+1);
        }
      }   
    });
    ansSet = nextAnsSet;
  }
  
  const ansList = Array.from(ansSet);
  ansList.sortByIntegers();
  console.log(ansList.length);
  console.log(ansList.oneLineString());
}

//my functions ------------------------------------

function getIntegers(lines) {
  return lines.shift().split(" ").map(function(e) {
    return Number(e);
  });
}

function getStrings(lines) {
  return lines.shift().split(" ");
}

function twoDimensionalArray(h, w, value) {
  const list = new Array(h);
  for(let i=0; i<h; i++) {
    list[i] = new Array(w).fill().map(function(e) {
      return (typeof value) == "object" ? Object.create(value) : value;
    });
  }
  return list;
}

Array.prototype.sortByIntegers = function() {
  this.sort(function(a, b) {
    return a - b;
  });
};

Array.prototype.oneLineString = function() {
  let str = "";
  this.forEach(function(e, i) {
    if(i > 0) str += " ";
    str += e;
  });
  return str;
};

main(require("fs").readFileSync("/dev/stdin", "utf8").split("\n"));