input: Write a function to concatenate two strings and return the length of the concatenated string.
  assert countChars("hello", "world") == 10
  assert countChars("foo", "bar") == 6
  assert countChars("python", "programming") == 18
output: def countChars(str1, str2):
      concatenated_str = str1 + str2
      return len(concatenated_str)