Step 1: Divide the number into separate digits:
4290 => 4 2 9 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 2 = 2
2 to 9 = 7
9 to 0 = 9
0 to 4 = 4
Step 3: Combine the filters to a string:
2 7 9 4 = 2794