Step 1: Divide the number into separate digits:
4677 => 4 6 7 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 6 = 2
6 to 7 = 1
7 to 7 = 0
7 to 4 = 3
Step 3: Combine the filters to a string:
2 1 0 3 = 2103