Given a string array words, find the maximum value of length(word[i]) * length(word[j]) where the two words do not share common letters. You may assume that each word will contain only lower case letters. If no such two words exist, return 0.

Example 1:


Given ["abcw", "baz", "foo", "bar", "xtfn", "abcdef"]
 Return 16
 The two words can be "abcw", "xtfn".

Example 2:


Given ["a", "ab", "abc", "d", "cd", "bcd", "abcd"]
 Return 4
 The two words can be "ab", "cd".

Example 3:


Given ["a", "aa", "aaa", "aaaa"]
 Return 0
 No such pair of words.