The Python program I used to make sure my brother's grades allowed him to get his Christmas present.

christmas.py

print("Welcome Jeremy, we've been waiting for you.")
print("We're going to find out if you've been naughty or nice.")
print("Enter your grades one line at a time, then put DONE")

cipher = "Orrn#wr#wkh#ohiw#ri#wkh#Dufdgh#Fdelqhw"

grades = []
grade = input()


while grade != "DONE":
  grades.append(grade[0])
  grade = input()

gpas = []

for g in grades:
  if g == 'A' or g == 'a':
    gpas.append(4.0)
  elif g == 'B' or g == 'b':
    gpas.append(3.0)
  elif g == 'C' or g == 'c':
    gpas.append(2.0)
  elif g == 'D' or g == 'd':
    gpas.append(1.0)
  else:
    gpas.append(0.0)

print("Did you lie? I will find out if you did...")

lied = input()

if lied == "yes" or lied == "y":
  print("Shame on you.")
  exit(32)

total_gpa = sum(gpas) / len(gpas)
print("Your total GPA is " + str(total_gpa))

if total_gpa > 3.0:
  treasure = ""
  for char in cipher:
    treasure += chr(ord(char) - 3)
  print(treasure)
else:
  print("You'll just have to try better next quarter.")