Step 1: Divide the number into separate digits:
3553 => 3 5 5 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 5 = 2
5 to 5 = 0
5 to 3 = 2
3 to 3 = 0
Step 3: Combine the filters to a string:
2 0 2 0 = 2020