import re,math
regex = re.compile(r'[a-z]*')
ans = 0
string = input()
string = str(string)
mo = regex.sub('0',string)
number = mo
math_len = len(number)
number = int(number)
for i in range(math_len):
    num = number % 10
    number = math.floor(number / 10)
    ans += num
print(ans)