zju 1006 Do the Untwist

zoj 1007 源代码。已经测试通过 AC-zoj 1007 source code. Has been tested by AC

The message to be encrypted is stored in plaintext. Given a key k, the encryption method works as follows. First convert the letters in plaintext to integer codes in plaincode according to the following rule: _ = 0, a = 1, b = 2, ..., z = 26, and . =