def FV(pv:float, r:float, n:float, m = 1):
  """
  FV(): A function to calculate Future Value.

  :param pv: Present Value
  :type pv: float
  :param r: Rate of Interest/Discount Rate (in decimals eg: 0.05 for 5%)
  :type r: float
  :param n: Number of Years
  :type n: float
  :param m: Frequency of Interest Calculation (eg: 2 for Semi-annually), defaults to 1.
  :type m: float
  :return: float, None for -ve values of m.
  :rtype: float

  --------
  """
  if(m<=0):return None
  return pv*((1+r/m)**(m*n))