N = ['0'] + list(input())
# print (N)
tmp1= len(N) - 1
ans = 0
while tmp1 >= 1:
    if N[tmp1] == '0':
        tmp1 -= 1
    elif N[tmp1] == '1' and N[tmp1 - 1] == '1': 
        while N[tmp1 - 1] == '1':
            N[tmp1] = '0'
            N[tmp1 - 1] = '0'
            tmp1 -= 1
        N[tmp1 - 1] = '1'
        tmp1 -= 1
        ans += 1
    elif N[tmp1] == '1' and N[tmp1 - 1] == '0':
        ans += 1
        tmp1 -= 1
    # print (N)

if N[0] == '1':
    ans += 1
print (ans)

# print (N)