S = input()
S = list(S[::-1] + "00")
ans = 0
car = False
n = len(S)
for i in range(n):
    if car:
        if S[i] == "0":
            S[i] = "1"
            car = False
        else:
            S[i] = "0"
    if S[i] == "1":
        ans += 1
        if S[i + 1] == "1":
            car = True
        else:
            car = False
print(ans)