Step 1: Divide the number into separate digits:
5439 => 5 4 3 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 4 = 1
4 to 3 = 1
3 to 9 = 6
9 to 5 = 4
Step 3: Combine the filters to a string:
1 1 6 4 = 1164