Generate Lexicographical Word Pairs

You are given a list of words. Your task is to remove any duplicates and then generate all unique pairs of words \( (a, b) \) such that \( a \) comes before \( b \) in lexicographical order (i.e., \( a < b \)).

The resulting pairs should be listed in lexicographical order. If no valid pair exists (i.e. when the list contains less than two unique words), no output should be produced.

Note: Each pair should be printed on a new line in the format: word1 word2.

inputFormat

The first line contains an integer \( n \) (\( n \geq 1 \)), representing the number of words. The second line contains \( n \) space-separated words.

outputFormat

For each valid pair \( (a, b) \) such that \( a < b \) in lexicographical order, output a single line with the two words separated by a space. If no valid pair exists, output nothing.

## sample

3
apple banana cherry

apple banana
apple cherry
banana cherry

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