S=list(map(int, input()))
res=[]
row=[]
row.append(S[0])
for i in range(1, len(S)):
    if S[i] == S[i-1]:
        row.append(S[i])
    else:
        res.append(row)
        row=[S[i]]
res.append(row)

count=0
ans=0
p=0
for num,i in enumerate(res):
  if i[0] == 1:
    count += len(i)
  else:
    if count == 1:
      count=0
      continue
    if count%2 == 0:
      ans += (count//2)*len(i)
    else:
      ans += (count//2)*len(i)
      count -= 1
print(ans)