Very badly designed !!! There is a severe overflow bug in the C++ random test cases. So the correct solution could not be accepted. Also, since the error of the overflow is dependent on the implementation. So I have to try several implementations to "fit" this kata.

If the author could not figure out how to make a bug free non-overflow solution, at least he can refine the problem description, for example, one can ask for the result modulo 1000007.

There are three kinds of string enclosing marks in javascript : double quote ("), single quote (') and apostrophe (`). When using apostrope, you can use expression in the string surrounded by ${}.

So instead of
var a = 3;
var b = "I've read " + a + " books.";

We can rewrite it as
var a = 3;
var b = `I've read ${a} books.`;

Good kata to learn this.

ES6 makes my life easier.