input: Write a function to print the Fibonacci series up to n numbers where n is a user input. If n is less than or equal to 0, print "Invalid input".
  assert fibonacci_series(10)==None
  assert fibonacci_series(5)==None
  assert fibonacci_series(0)=="Invalid input"
  assert fibonacci_series(-3)=="Invalid input"
  assert fibonacci_series(1)==None
output: def fibonacci_series(n):
      if n <= 0:
          print("Invalid input")
          return
      a, b = 0, 1
      for _ in range(n):
          print(a, end=' ')
          a, b = b, a + b
      print()