[计] alert before overwriting cells

duì dān yuán fù gài qián bào jǐng ㄉㄨㄟˋ ㄉㄢ ㄩㄢˊ ㄈㄨˋ ㄍㄞˋ ㄑㄧㄢˊ ㄅㄠˋ ㄐㄧㄥˇ