Step 1: Divide the number into separate digits:
6339 => 6 3 3 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 3 = 3
3 to 3 = 0
3 to 9 = 6
9 to 6 = 3
Step 3: Combine the filters to a string:
3 0 6 3 = 3063