function book(arr) {
  let shelf = arr.shift().split("&");
  let commands = arr.shift();
  while (commands !== "Done") {
    let currComamnds = commands.split(" | ");
    let command = currComamnds[0];
    let token = currComamnds[1];
    let token1 = currComamnds[2]

    switch (command) {
      case "Add Book": add(command, token); break;
      case "Take Book": take(command, token); break;
      case "Swap Books": swap(command, token, token1); break;
      case "Insert Book": insert(command, token); break;
      case "Check Book":check (command, token); break;
    }
    commands = arr.shift()



    function add(command, token) {
      if (!shelf.includes(token)) {
        shelf.unshift(token);
      }
    }

    function take(command, token) {
      if (shelf.includes(token)) {
        let index = shelf.indexOf(token);
        shelf.splice(index, 1);
      }
    }

    function swap(command, token, token1) {
      if (shelf.includes(token) && shelf.includes(token1)) {
        let index1 = shelf.indexOf(token);
        let index2 = shelf.indexOf(token1);


        let temp = shelf[index1];
        let temp2=shelf[index2]
        shelf[index1] = temp2;
        shelf[index2]=temp

      }
    }

    function insert(command, token) {
      if (!shelf.includes(token)) {
        shelf.push(token);
      }
    }

    function check(command, token) {
      let index = Number(token)
      let book
      if (index>=0 && index < shelf.length) {
         book = shelf.splice(index, 1)

      }
      if(!shelf.includes(book)) {
        console.log(book[0]);
      }

      shelf.splice(index,0,book)

    }

  }
  console.log(shelf.join(", "));
}