}
    // Efficiently multiply all the intermediate products together.
    return listProduct(bignums).shiftLeft(shift);
  }

  static BigInteger listProduct(List<BigInteger> nums) {
    return listProduct(nums, 0, nums.size());
  }

  static BigInteger listProduct(List<BigInteger> nums, int start, int end) {
    switch (end - start) {
      case 0:
        return BigInteger.ONE;