added Exercise 14

ex_14.py

@@ -0,0 +1,18 @@
+from util.io import readvalue
+
+
+def fibonacci(n):
+	if(n in (0,1)):
+		return 1
+	return fibonacci(n - 1) + fibonacci(n - 2)
+
+if( __name__ == "__main__"):
+	
+	def nonnegative_int(s):
+		i = int(s)
+		if(i < 0):
+			raise ValueError("{} is smaller than zero".format(i))
+		return i
+
+	n = readvalue("n > ", nonnegative_int)
+	print("fibonacci(", n, ") = ", fibonacci(n))