N = list(map(int,list(input())))
N.reverse()
NN = len(N)
ans = 0
cnt = 0
for i in range(NN):
    if N[i] == 1:
        cnt += 1
    else:
        if cnt == 0:
            continue
        elif cnt == 1:
            cnt = 0
            ans += 1
        else:
            cnt = 1
            ans += 1

if cnt == 0:
    pass
elif cnt == 1:
    cnt = 0
    ans += 1
else:
    cnt = 1
    ans += 2
print(ans)