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

L.reverse()
L.append(0)
n = len(L)
ans = 0
for i in range(n):
    if L[i] == 1:
        if i == n - 1:
            ans += 1
        elif L[i + 1] == 0:
            ans += 1
            L[i] = 0
        else:
            while L[i] == 1:
                L[i] = 0
                i += 1
            L[i] = 1
            ans += 1
print(ans)