题目：输入一个英文句子，翻转句子中单词的顺序，但单词内字符的顺序不变。句子中单词以空格符隔开。

为简单起见，标点符号和普通字母一样处理。

例如输入“I am a student.”，则输出“student. a am I”。

-Title: Enter an English sentence, flip the order of the words in the sentence, but the word within the character of the same order. Sentence words separated by a space character. For simplicity, punctuation and letters processed. For example, enter " I am a student."　Output " student. A am I" .