#!usr/bin/env python3

from collections import defaultdict

from collections import deque

from heapq import heappush, heappop

import sys

import math

import bisect

import random

def LI(): return list(map(int, sys.stdin.readline().split()))

def I(): return int(sys.stdin.readline())

def LS():return list(map(list, sys.stdin.readline().split()))

def S(): return list(sys.stdin.readline())[:-1]

def IR(n):

    l = [None for i in range(n)]

    for i in range(n):l[i] = I()

    return l

def LIR(n):

    l = [None for i in range(n)]

    for i in range(n):l[i] = LI()

    return l

def SR(n):

    l = [None for i in range(n)]

    for i in range(n):l[i] = S()

    return l

def LSR(n):

    l = [None for i in range(n)]

    for i in range(n):l[i] = LS()

    return l

sys.setrecursionlimit(1000000)

mod = 1000000007



#A

def A():

    n,a,b = LI()

    print((min(n*a,b)))

    return



#B

def B():

    s = S()

    print((s.count("1")))

    return



#C

def C():

    return



#D

def D():

    return



#E

def E():

    return



#F

def F():

    return



#G

def G():

    return



#H

def H():

    return



#I

def I_():

    return



#J

def J():

    return



#Solve

if __name__ == "__main__":

    B()

#!usr/bin/env python3

from collections import defaultdict,deque

from heapq import heappush, heappop

from itertools import permutations

import sys

import math

import bisect

def LI(): return [int(x) for x in sys.stdin.readline().split()]

def I(): return int(sys.stdin.readline())

def LS():return [list(x) for x in sys.stdin.readline().split()]

def S():

    res = list(sys.stdin.readline())

    if res[-1] == "\n":

        return res[:-1]

    return res

def IR(n):

    return [I() for i in range(n)]

def LIR(n):

    return [LI() for i in range(n)]

def SR(n):

    return [S() for i in range(n)]

def LSR(n):

    return [LS() for i in range(n)]



sys.setrecursionlimit(1000000)

mod = 1000000007



def solve():

    s = eval(input())

    print((s.count("1")))

    return



#Solve

if __name__ == "__main__":

    solve()

#!usr/bin/env python3
from collections import defaultdict
from collections import deque
from heapq import heappush, heappop
import sys
import math
import bisect
import random


def LI():
    return list(map(int, sys.stdin.readline().split()))


def I():
    return int(sys.stdin.readline())


def LS():
    return list(map(list, sys.stdin.readline().split()))


def S():
    return list(sys.stdin.readline())[:-1]


def IR(n):
    l = [None for i in range(n)]
    for i in range(n):
        l[i] = I()
    return l


def LIR(n):
    l = [None for i in range(n)]
    for i in range(n):
        l[i] = LI()
    return l


def SR(n):
    l = [None for i in range(n)]
    for i in range(n):
        l[i] = S()
    return l


def LSR(n):
    l = [None for i in range(n)]
    for i in range(n):
        l[i] = LS()
    return l


sys.setrecursionlimit(1000000)
mod = 1000000007
# A
def A():
    n, a, b = LI()
    print((min(n * a, b)))
    return


# B
def B():
    s = S()
    print((s.count("1")))
    return


# C
def C():
    return


# D
def D():
    return


# E
def E():
    return


# F
def F():
    return


# G
def G():
    return


# H
def H():
    return


# I
def I_():
    return


# J
def J():
    return


# Solve
if __name__ == "__main__":
    B()

#!usr/bin/env python3
from collections import defaultdict, deque
from heapq import heappush, heappop
from itertools import permutations
import sys
import math
import bisect


def LI():
    return [int(x) for x in sys.stdin.readline().split()]


def I():
    return int(sys.stdin.readline())


def LS():
    return [list(x) for x in sys.stdin.readline().split()]


def S():
    res = list(sys.stdin.readline())
    if res[-1] == "\n":
        return res[:-1]
    return res


def IR(n):
    return [I() for i in range(n)]


def LIR(n):
    return [LI() for i in range(n)]


def SR(n):
    return [S() for i in range(n)]


def LSR(n):
    return [LS() for i in range(n)]


sys.setrecursionlimit(1000000)
mod = 1000000007


def solve():
    s = eval(input())
    print((s.count("1")))
    return


# Solve
if __name__ == "__main__":
    solve()

-from collections import defaultdict -from collections import deque +from collections import defaultdict, deque +from itertools import permutations -import random -    return list(map(int, sys.stdin.readline().split())) +    return [int(x) for x in sys.stdin.readline().split()] -    return list(map(list, sys.stdin.readline().split())) +    return [list(x) for x in sys.stdin.readline().split()] -    return list(sys.stdin.readline())[:-1] +    res = list(sys.stdin.readline()) +    if res[-1] == "\n": +        return res[:-1] +    return res -    l = [None for i in range(n)] -    for i in range(n): -        l[i] = I() -    return l +    return [I() for i in range(n)] -    l = [None for i in range(n)] -    for i in range(n): -        l[i] = LI() -    return l +    return [LI() for i in range(n)] -    l = [None for i in range(n)] -    for i in range(n): -        l[i] = S() -    return l +    return [S() for i in range(n)] -    l = [None for i in range(n)] -    for i in range(n): -        l[i] = LS() -    return l +    return [LS() for i in range(n)] -# A -def A(): -    n, a, b = LI() -    print((min(n * a, b))) -    return -# B -def B(): -    s = S() +def solve(): +    s = eval(input()) -    return - - -# C -def C(): -    return - - -# D -def D(): -    return - - -# E -def E(): -    return - - -# F -def F(): -    return - - -# G -def G(): -    return - - -# H -def H(): -    return - - -# I -def I_(): -    return - - -# J -def J(): -    B() +    solve()