Blood Types

When a person receives a blood transfusion, it is essential to make sure that the donor's blood type is compatible with the receiver's blood type. Receiving a blood type that is not compatible with your own can be life-threating, so blood banks always make sure to note the type of blood they receive from donors so that they can ensure a safe transfusion.

Blood types are named according to three factors: presence of antigen A, presence of antigen B, and presence of Rh factor. If antigen A is found, the blood type includes the letter "A". If antigen B is found, the blood type includes the letter "B". And if the Rh factor is present, the blood type ends with "+"; otherwise, it ends with "-". If neither antigen A nor antigen B are found, the blood type includes the letter "O".

For example, a person with only antigen A would have the blood type "A-". A person with both antigens A and B and the Rh factor would have blood type "AB+", and a person wih only the Rh factor would have blood type "O+".

The rules for giving and receiving blood are as follows:

• A person with antigen A may only give blood to another person with antigen A.
• A person with antigen B may only give blood to another person with antigen B.
• A person with the Rh factor may only give blood to another person with the Rh factor.
• A person with none of the above factors (O-) can give blood to anyone.

Write a function that takes in a donor's and receiver's blood types as strings and returns whether or not the donor can safely give blood to the receiver, according to the rules above.

Examples

can_give_blood("O+", "A+") ➞ True

can_give_blood("A-", "B-") ➞ False

can_give_blood("A-", "AB+") ➞ True

Notes

• All letters are capital.
• Each blood type will be one of the following strings: "O+", "O-", "A+", "A-", "B+", "B-", "AB+", "AB-".