n = list('00' + input())
r = 0
for i in range(1, len(n))[::-1]:
    if n[i] == '1':
        n[i] = '0'
        i -= 1
        if n[i] == '1':
            while n[i] == '1':
                n[i] = '0'
                i -= 1
            n[i] = '1'
        r += 1
print(r)