Step 1: Divide the number into separate digits:
4190 => 4 1 9 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 1 = 3
1 to 9 = 8
9 to 0 = 9
0 to 4 = 4
Step 3: Combine the filters to a string:
3 8 9 4 = 3894