(a_n a_{n-1}\dots a_1 a_0. a_{-1}a_{-2}\dots a_{-k})_p=\sum_{j=-k}^n {a_j\cdot p^j}=\sum_{j=0}^n {a_j\cdot p^j} + \sum_{j=1}^k{\frac{a_{-j}}{p^j}}