def remove_duplicates(s):
	"""
	Given a string, remove duplicate characters, retaining only the first time for each unique character.
	Example: helloh -> helo
	"""
	unique_chars = set()
	new_string = ""
	for char in s:
		if char not in unique_chars:
			new_string += char
			unique_chars.add(char)
	return new_string