Engineers have taken over the university’s English department! As part of their plan to dominate the university, they have employed you to write their nefarious software. Their goal is to eliminate all duplicated words from all texts in the English department, because, as they say, “duplicated words are duplicated work” and “duplicated work wastes money.” Actually, what they would really say is “duplicated words are . work” and “. . wastes money”. This is what your program should do – remove all duplicate words and replace them with a period.

-----Input-----
Input is a textbook with at most $2000$ lines. Each line contains up to $100$ characters. Punctuation does not appear (it has already been removed by another programmer); words are made up of up to $20$ lower and uppercase characters (a–z). There are at most $20000$ total words in the input. Each pair of adjacent words is separated by a single space. Case does not matter when comparing words for duplicates (i.e. ‘Book’ and ‘book’ and ‘bOoK’ should be considered the same word). Input ends at end of file.

-----Output-----
Print each word the first time it appears, but thereafter if that word appears again print a period.

-----Examples-----
Sample Input:
Engineering will save the world from inefficiency
Inefficiency is a blight on the world and its
humanity
Sample Output:
Engineering will save the world from inefficiency
. is a blight on . . and its
humanity

Difficulty: introductory

Starter code:

Solutions: