Step 1: Divide the number into separate digits:
5140 => 5 1 4 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 1 = 4
1 to 4 = 3
4 to 0 = 4
0 to 5 = 5
Step 3: Combine the filters to a string:
4 3 4 5 = 4345