### N-bonacci

The classic Fibonacci sequence starts with 0 and 1, after which each term is the sum of the previous two.
Let's generalize this to the *N*-bonacci sequence, where the first *N* terms are 0, 1, …, *N* - 1
and each later term is the sum of the *N* previous terms.

Write a function called `nbonacci`

which takes two `int`

parameters, *N* and the zero-based term index.
*N* will always be positive and the term index will always be nonnegative.

For example, `nbonacci(2, 4)`

should return 3 because the 2-bonacci sequence
(which is the classic Fibonacci sequence) begins 0, 1, (0 + 1) = 1, (1 + 1) = 2, (1 + 2) = **3**.
`nbonacci(3, 5)`

should return 11 because the 3-bonacci sequence begins 0, 1, 2, (0 + 1 + 2) = 3, (1 + 2 + 3) = 6, (2 + 3 + 6) = 11.