n = input()
ans = 0
ln = len(n)
oc = 0
zc = 0
for i in range(ln-1,-1,-1):
    if n[i] == "1":
        oc += 1
    else:
        if i != ln-1 and n[i+1] == "0":
            ans += min(oc,zc+2)
            zc = 0
            oc = 0
        else:
            zc += 1

ans += min(oc,zc+2)
print(ans)