class Compress:
    def __init__(self,array):
        """ A=[(a,degeneracy),...] """
        S=[0]
        self.array=array[:]
        self.A=[]
        for a, cnt in array:
            S.append(S[-1]+cnt)
            self.A.append(a)
        self.S=S[1:]

    def __getitem__(self, i):
        j=bisect_left(self.S,i+1)
        return self.A[j]

    def sum(self, i):
        """ sum in [0,i) """
        j=bisect_left(self.S,i)
        res=0
        q=0
        for k in range(j):
            res+=self.A[k]*(self.S[k]-q)
            q=self.S[k]
        print(j, res)
        if j>0: res+=self.A[j]*(i-self.S[j-1])
        else: res+=self.A[j]*(i)
        return res

    def sort(self):
        S=[0]
        self.A=[]
        for a, cnt in sorted(self.array):
            S.append(S[-1]+cnt)
            self.A.append(a)
        self.S=S[1:]

    def __iter__(self):
        l=0
        for i in range(self.S[-1]):
            if i==self.S[l]:
                l+=1
            yield self.A[l]

    def __str__(self):
        return " ".join(list(map(str, self)))

def deg(A):
    """
    連続して続く文字を圧縮する（※Counterではない）
    [1,1,1,2,2,2,3] -> [(1,3),(2,3),(3,1)]
    """
    res=[]
    a0, cnt=A[0], 1
    for a in A[1:]+[None]:
        if a!=a0: res.append((a0,cnt)); cnt=1
        else: cnt+=1
        a0=a
    return res


def bit_rep(bit,N):
    return format(bit, "0" + str(N) + "b")
def bits_rep(bits,N):
    return [format(bit, "0" + str(N) + "b") for bit in bits]


###############################################################
import sys
from bisect import *
input = sys.stdin.readline

N=input().rstrip()
S=list(map(int,N))
data=deg(S)
res=0
for i in range(len(data)):
    a,cnt=data[i]
    if a==0:continue
    if i!=0 and data[i-1][1]==1:
        res+=min(1,cnt)
    else:
        res+=min(2,cnt)
print(res)