S = [int(c) for c in input()]
N = len(S)
zero_ct = 0
ans = 0
for i in range(N-1, -1, -1):
    if S[i] == 0: zero_ct += 1
    else:
        if i != N-1 and S[i+1] == 1:
            ans += zero_ct

print(ans)