input: Write a function to calculate the sum of the series 1 + ½ + ⅓ + ... + 1/n. The function should take an integer n as input and return the sum of the series. If the input is invalid (e.g., negative number), the function should return 0.
  assert seriesSum(5) == 2.283333333333333
  assert seriesSum(3) == 1.8333333333333333
  assert seriesSum(0) == 0
  assert seriesSum(-1) == 0
output: def seriesSum(n):
      if n <= 0:
          return 0
      return sum(1/i for i in range(1, n+1))