input: Write a function to calculate a simple hash value for a given string using a custom algorithm.
  assert calculate_hash("hello") == 7
  assert calculate_hash("world") == 3
  assert calculate_hash("test") == 2
output: def calculate_hash(s):
      hash_value = 0
      for char in s:
          hash_value += ord(char)
      return hash_value % 10