def who_is_missing(file_name):
	opened_file = open(file_name, "r")
	file = opened_file.read()
	list = file.split(',')
	max = '0'
	for k in list:
		if k > max:
			max = k
	for i in range (1, int(max) + 1):
		if str(i) not in list and str(i) > '0' and str(i) < str(max):
			opened_file.close()
			file = open(file_name, "r+")
			num = str(i)
			file.write(num)
			return i


def main():
	pass

if __name__ == "__main__":
    main()