def group_when(xs, pred):
    res = []
    a = []
    for x in xs:
        if not a or pred(a[-1], x):
            a.append(x)
        else:
            res.append(a)
            a = [x]
    if a:
        res.append(a)
    return res


S = input()

xs = [int(c) for c in S]
gg = group_when(xs, lambda a, b: a == b)
one = 0
ans = 0
for g in gg:
    d = g[0]
    n = len(g)
    if d == 0:
        ans += (one // 2) * n
        one = (one // 2) * 2
    elif d == 1:
        one += n

print(ans)