S = list(input())
N = len(S)
if N <= 2:
    exit(print(0))

ans = 0
wa = 0
for i in range(N - 1, -1, -1):

    if S[i] == '0':
        wa += 1
    else:
        if i + 3 <= N and S[i : i + 3] == ["1", "1", "0"]: 
            ans += wa
        elif i > 0 and S[i - 1] == '0':
            wa = 0
    
    # print(ans, wa)

print(ans)