input: Write a function to multiply two input numbers and print the result. If either of the input numbers is not a number then return "Invalid input".
  assert multiply(3, 4)=="12"
  assert multiply(5, 0)=="0"
  assert multiply(7, -2)=="-14"
  assert multiply("3", 2)=="Invalid input"
  assert multiply(3, "a")=="Invalid input"
output: def multiply(a, b):
      if not isinstance(a, (int, float)) or not isinstance(b, (int, float)):
          return "Invalid input"
      return str(a * b)