def digit_sum(n):
	sum = 0
	new_n = n
	while new_n > 10:
		s = n%10
		new_n = (new_n - s)//10
		sum = sum + s
	else:
		sum = sum + new_n
		print (sum)

#z = int (input ("Введите число:"))
digit_sum(2564)