S=input()
A=[]
from collections import deque
d=deque()

N=len(S);a='!';c=0
for i in range(N):
  s=S[i]
  if s==a:
    c+=1
  else:
    if c!=0:
      d.append((a,c))
    a=s;c=1 
d.append((a,c))
if d[-1][0]=='1':
  d.append(('0',0))
  
if d[0][0]=='0':
  d.popleft()

ans=0
while d:
  _,p=d.popleft()
  _,q=d.popleft()
  ans+=(p//2)*q 
  if d:
    a,b=d.popleft()
    d.appendleft((a,b+p-p%2))
print(ans)