N = [0] + [int(x) for x in input()]
cur = len(N) - 1
ans = 0
while cur:
    if N[cur] == N[cur - 1] == 1:
        ans += 1
        while N[cur]:
            N[cur] = 0
            cur -= 1
        N[cur] = 1
    else:
        cur -= 1
ans += N.count(1)
print(ans)