Given two string arrays words1 and words2, return the number of strings that appear exactly once in words1 and exactly once in words2.

Constraints:

• $1 \leq$ words1.length, words2.length $\leq 1000$

• $1 \leq$ words1[i].length, words2[j].length $\leq 30$

• words1[i] and words2[j] consist only of lowercase English letters.

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