Snuke has a grid consisting of three squares numbered 1, 2 and 3. In each square, either `0` or `1` is written. The number written in Square i is s_i.  Snuke will place a marble on each square that says `1`. Find the number of squares on which Snuke will place a marble.

import sys
from sys import stdin
input = stdin.readline
 
 
def main(args):
    s = input().strip()
    print(s.count('1'))
s = input()
ans = 0
for i in range(3):
    if s[i] == "1":
        ans += 1
print(ans) 