Exception resolve issue #475

Author: Kushagra9399

pydatastructs/multi_threaded_algorithms/fibonacci.py

@@ -12,6 +12,8 @@ class Fibonacci:
     """
 
     def __init__(self, n, backend='python'):
+        if n<0:
+            raise ValueError("n cannot be negative")
         self.n = n
         self.backend = backend
         self.result = [None] * (n + 1)  # To store Fibonacci numbers