That's a thing with us Europeans - especially if you don't want to perfectly adopt a British or American accent. This is when you end up with the "euro accent" - you're perfectly fluent in English, without the accent of your native language, but since its neither British nor American English, it sounds just the slightest bit different.
Simple, really. Abs(x-y) is the difference between the two numbers, absolute, so positive value. So, adding abs(x-y) to the smaller of the two numbers turns it into the bigger number. Plus the bigger number, now you have 2 times the bigger number