Step 1: Divide the number into separate digits:
4500 => 4 5 0 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 5 = 1
5 to 0 = 5
0 to 0 = 0
0 to 4 = 4
Step 3: Combine the filters to a string:
1 5 0 4 = 1504