def pv_perpetuity_due(c,r):
    """Objective: estimate present value of a perpetuity due
                  i.e., 1st cash flow occurs today
          c: period payment
          r: discount rate
          e.g.,
          >>>pv_perpetuity_due(30000,0.08)
          405000.0
    """
    return(c/r*(1+r))