Fibonacci Numbers

Statement

Implement a function to find the n$^{th}$ Fibonacci number in the Fibonacci sequence.

Fibonacci numbers form a sequence known as the Fibonacci sequence, where each number is the sum of two preceding ones, starting from $0$ and $1$.

The Fibonacci numbers are defined as:

• $F_0= 0$
• $F_1= 1$
• $F_n= F_{n-1} + F_{n-2}$, for $n \geq 2$

Based on the definition above, the first $10$ Fibonacci numbers starting, from the $0^{th}$, are: $0, \space 1, \space 1, \space 2, \space 3, \space 5, \space 8, \space 13, \space 21, \space 34$.

Sample input

8

Expected output

21