Just something I'm doing at home

Line 13 SyntaxError: 'return' outside function

I am trying to return the final number for an addition

```
print "Hello and welcome to Alfie's calculator Alpha Version One Point Oh"
first_num = int(raw_input("What is your first number?"))
print "Please use 'add' or 'subtract'"
operation = (raw_input("Write the operation you would like to use."))
second_num = int(raw_input("What is your second number?"))
final_num_add = first_num + second_num
final_num_subtract = first_num - second_num
if len(first_num) > 0 and not first_num.isalpha() and len(operation) > 0 and not operation.isalpha() and len(second_num) > 0 and not second_num.isalpha():
if operation == add:
return final_num_add
elif operation == subtract:
return final_num_subtract
else:
return "error: wrong operation input"
else:
return "error: incorrect characters for num input"
```