import sys
pin = sys.stdin.readline

def ST(): return pin().rstrip()
def IN(): return int(pin())
def IM(): return map(int, pin().split())
def IL(): return list(map(int, pin().split()))
def SR(n:int): return [pin().rstrip() for _ in range(n)]
def IMatrix(n:int): return [IL() for _ in range(n)]

##-----------------
import random
import math
import bisect
import itertools
from collections import defaultdict, deque
#from sortedcontainers import SortedList
##-----------------

S = ST()
max_right = 0
ans = 0
flag = False
for i in range(len(S)-1, 0, -1):
	if flag:
		flag = False
		continue
	if S[i] == '0':
		max_right += 1
	elif S[i-1:i+1] == '11':
		ans += max_right
		flag = True
print(ans)