def magical_well(a, b, n, s=0):
    return s if n==0 else magical_well(a+1,b+1,n-1,s+a*b)

'''
Task

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 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.

Input/Output

    [input] integer a

    Constraints: 1 ≤ a ≤ 2000

    [input] integer b

    Constraints: 1 ≤ b ≤ 2000

    [input] integer n

    The number of magic marbles in your possession, a non-negative integer.

    Constraints: 0 ≤ n ≤ 5

    [output] an integer
'''