Sorry for the title because i am not sure what it should be. I was given this task where i had to select two subject from the list and add the price up and my codes are: 

```
print("choose two subjects")
print("English $100")
print("Math $75")
print("Science $125")
print("Stem $200")
a = input("Choose two subjects: ")
a = a.split()
for x in a:
  x = x.lower()
  print(x)
  if x == "english":
    eng = 100
  elif x is not "english":
    eng = int(0)

  elif x == "science":
    sci = 125
  elif x is not "science":
    sci = int(0)

  elif x == "stem":
    stem = 200
  elif x is not "stem":
    stem = int(0)

  elif x == "math":
    math = 100
  elif x is not "math":
    math = int(0)
print(eng + sci + math + stem)

```

i have an error when i type in english and science which outputs "math" is not defined