CodeSignal: Magic Well

magicWell.js

/*

You are standing at a magical well. It has two positive integers written on it: a and b. Each time you cast a magic marble into the well, it gives you a * b dollars and then both a and b increase by 1. You have n magic marbles. How much money will you make?

Example

For a = 1, b = 2, and n = 2, the output should be
magicalWell(a, b, n) = 8.

You will cast your first marble and get $2, after which the numbers will become 2 and 3. When you cast your second marble, the well will give you $6. Overall, you'll make $8. So, the output is 8.

*/

function magicalWell(a, b, n) {
    let total = 0;
    for(let i = 0; i < n; i++) {
        total = a * b + total;
        a++;
        b++;
    }
        
    return total;
}