def RunLengthEncoding(S):
    res = []
    N = len(S)
    i = 0
    while i < N:
        cnt = 1
        while i < N - 1 and S[i] == S[i + 1]:
            cnt += 1
            i += 1
        res.append(cnt)
        i += 1
    return res


S = input()
R = RunLengthEncoding(S)
if S[-1] == "0":
    R.pop()
R.reverse()


X = min(2, R[0])
Y = 0
for zero, one in zip(R[::2], R[1::2]):
    nX = min(X + min(2, one), Y + zero + 2)
    nY = min(X, Y + zero)
    X, Y = nX, nY
print(X)