N = list(input())
N = N[::-1]

ans = 0

i = 0
while i < len(N):
    if N[i] == "1":
        j = i
        while j < len(N) and N[j] == "1":
            j += 1
        ans += 1
        if j - i == 1:
            i = j + 1
        else:
            if j == len(N):
                ans += 1
                break
            else:
                N[j] = "1"
                i = j
print(ans)