refactored the prb page and added fib seqq

problems/fibonacisequence/description.md

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+## Fibonacci Number
+
+Write a function called `fibonacci` that takes a non-negative integer `n` as input and returns the **n-th Fibonacci number**.
+
+The Fibonacci sequence is defined as:
+
+* `F(0) = 0`
+* `F(1) = 1`
+* `F(n) = F(n-1) + F(n-2)` for `n > 1`
+
+### Function Signature:
+
+```python
+def fibonacci(n):
+    # return your solution
+```
+
+#### Requirements
+
+* The function should return the `n`-th number in the Fibonacci sequence.
+* If `n` is less than `0`, print `"Incorrect input"`.
+* Your function will be tested with:
+
+  * Base cases (`n = 0` and `n = 1`)
+  * Small values of `n`
+  * Larger values of `n` (e.g., 9)
+  * Multiple test cases in sequence
+
+#### Example:
+
+```python
+fibonacci(0)   # returns 0
+fibonacci(1)   # returns 1
+fibonacci(2)   # returns 1
+fibonacci(3)   # returns 2
+fibonacci(5)   # returns 5
+fibonacci(9)   # returns 34
+```
+
+You can copy this into your problem’s solution description.