The single example given is too trivial. The question require another with larger values so that the wrapped values from mod arithmetic are visible. This is where I was caught out and I feel cheated and the exercise was a waste of time. There is another general issue involving using mod arithmetic. Unless it is required for the Maths involved in the problem why create test cases whose outputs will overflow the native machine numerical limits? Why do this and then require mod arithmetic so that so wrapped nonsense value is required for the answer? I didnt think much of the editorial either.