Valid Likes Checker

You are given a number of likes submitted to a social network. Each like is represented by two integers: a user id (uid) and a post id (pid). Your task is to determine whether all the likes are valid. A like is considered valid if the same user has not liked the same post more than once. In other words, if any (uid, pid) pair appears more than once, then the likes are invalid.

If all likes are unique, output "VALID"; otherwise, output "INVALID".

inputFormat

The first line of input contains a single integer \(n\) (the number of likes). Each of the following \(n\) lines contains two integers \(uid\) and \(pid\), which represents a user's like on a post.

\(1 \leq n \leq 10^5\)

outputFormat

Print a single line: "VALID" if all likes are unique, or "INVALID" if a duplicate like is found.

## sample

3
1 101
2 101
1 102

VALID

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