def readints():
  return list(map(int, input().split()))

def deep_recursion():
  import sys
  import pypyjit  # type: ignore
  sys.setrecursionlimit(550000)
  pypyjit.set_param('max_unroll_recursion=-1')

def main():
  S = input()
  n = len(S)
  ans = 0
  zero = 0
  ones = 0
  for i in range(n-1, -1, -1):
    if S[i] == '1':
      ones += 1
      if ones == 2:
        ones = 0
        ans += zero
    else:
      zero += 1
  print(ans)


if __name__ == '__main__':
  # deep_recursion()
  main()