public static BigInteger divide(BigInteger p, BigInteger q, RoundingMode mode) {
    BigDecimal pDec = new BigDecimal(p);
    BigDecimal qDec = new BigDecimal(q);
    return pDec.divide(qDec, 0, mode).toBigIntegerExact();
  }

  /**
   * Returns {@code n!}, that is, the product of the first {@code n} positive integers, or {@code 1}
   * if {@code n == 0}.
   *