def magicalWell(a, b, n):
    return sum((a+i)*(b+i) for i in range(n))

print(magicalWell(6,5,3))

'''
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.
'''
