text: # -*- coding: utf-8 -*-
  
  A = float(input())
  
  if 0 < A <= 2000:
      print("Isento")
  else:
      if 2000 < A <= 3000:
          tax = (A-2000) * 0.08
      if 3000 < A <= 4500:
          tax = 1000 * 0.08
          tax += (A-3000) * 0.18
      if 4500 < A:
          tax = 1000 * 0.08
          tax += 1500 * 0.18
          tax += (A-4500) * 0.28
      print("R$ %.2f"%tax)