def f(n,k=0):
    if n=="" : return 0
    t = ((-1)**(len(n)-1))*int(n[len(n)-1]) + f(n[:-1],k+1)
    if k == 0:
        return f(str(abs(t)),k+1) == 0
    return t

print(f("11"))
print(f("12"))
print(f("22"))
print(f("0"))
print(f("121"))
print(f("110"))