input: Write a function to calculate the sum of the series 1 + ½ + ⅓ + ... + 1/n. If the input number n is valid, the function should return the sum of the series. If n is less than 1, the function should return 0.
  assert seriesSum(5) == 2.283333333333333
  assert seriesSum(1) == 1
  assert seriesSum(0) == 0
  assert seriesSum(-1) == 0
  assert seriesSum(10) == 2.9289682539682538
output: def seriesSum(n):
      if n < 1:
          return 0
      return sum(1/i for i in range(1, n+1))