Step 1: Divide the number into separate digits:
8558 => 8 5 5 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 5 = 3
5 to 5 = 0
5 to 8 = 3
8 to 8 = 0
Step 3: Combine the filters to a string:
3 0 3 0 = 3030