L = list(map(int, list(input())))

L.reverse()
n = len(L)
Seq = []
if L[0] == 0:
    Seq.append(0)
res = 1
for i in range(1, n):
    if L[i] == L[i - 1]:
        res += 1
    else:
        Seq.append(res)
        res = 1
    if i == n - 1:
        Seq.append(res)
m = len(Seq)
ans = 0
seq0, seq1 = 0, 0
for i in range(0, m, 2):
    if i == m - 1:
        seq1 += Seq[i]
        seq0 = 0
    else:
        seq1 += Seq[i]
        seq0 += Seq[i + 1]
    if seq1 == 0:
        seq0 = 0
        continue
    if seq1 == 1:
        ans += 1
        if seq0 == 1:
            seq1 = 1
            seq0 = 0
        else:
            seq1 = 0
            seq0 = 0
    elif seq1 >= 2:
        if seq0 == 1:
            ans += 1
            seq1 = 1
        else:
            ans += 2
            seq1 = 0
        seq0 = 0
print(min(ans, sum(L)))