Step 1: Divide the number into separate digits:
9050 => 9 0 5 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 0 = 9
0 to 5 = 5
5 to 0 = 5
0 to 9 = 9
Step 3: Combine the filters to a string:
9 5 5 9 = 9559