n=list(map(int,list(input())))
n2=n[::-1]+[0]
n3=[]
# print(n,n2)
count=0
for i in range(len(n2)-1):
    if n2[i]==2:
        n2[i]=0
        n2[i+1]+=1
    elif n2[i]==1 and n2[i+1]==1:
        n2[i],n2[i+1]=0,2
        count+=1
    else:pass
for i in n2:
    if i==1:
        count+=1
print(count)