Step 1: Divide the number into separate digits:
6943 => 6 9 4 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 9 = 3
9 to 4 = 5
4 to 3 = 1
3 to 6 = 3
Step 3: Combine the filters to a string:
3 5 1 3 = 3513