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?

function magicalWell(a, b, n) {
    var res = 0;
while (n > 0){
    res += a * b; 
    a++;
    b++;
    n--;
}
    return res;
}