Step 1: Divide the number into separate digits:
8385 => 8 3 8 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 3 = 5
3 to 8 = 5
8 to 5 = 3
5 to 8 = 3
Step 3: Combine the filters to a string:
5 5 3 3 = 5533