N = list(input())

ans = 0

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