Write an algorithm to implement encrypting capital letters using the Caesar cipher. Use all capital letters to implement the encryption algorithm for the Caesar cipher by shifting three letters forward in the alphabet. This can be represented by using the following equation: set_shifted_position = ((alphabet_position + 3) mod 26) + 1.
Your instructions:
1. You should add all letters to the alphabetList.
2. Ask the user to enter some text in UPPERCASE for encryption.
3. The input text should be encrypted using the above equation. For example, if the user inputs "APPLE", then it will be encrypted as "ETTP".
4. Write your algorithm and then implement the algorithm using OUBUILD.
5. Provide screenshots for the input and output results.