You are playing a game that contains multiple characters, and each of the characters has two main properties: attack and defense. You are given a 2D integer array `properties` where `properties[i] = [attacki, defensei]` represents the properties of the `ith` character in the game.

A character is said to be weak if any other character has both attack and defense levels strictly greater than this character's attack and defense levels. More formally, a character `i` is said to be weak if there exists another character `j` where `attackj > attacki` and `defensej > defensei`.

Return the number of weak characters.

Example 1:

    Input: properties = [[5,5],[6,3],[3,6]]
    Output: 0
    Explanation: No character has strictly greater attack and defense than the other.

Example 2:

    Input: properties = [[2,2],[3,3]]
    Output: 1
    Explanation: The first character is weak because the second character has a strictly greater attack and defense.

Example 3:

    Input: properties = [[1,5],[10,4],[4,3]]
    Output: 1
    Explanation: The third character is weak because the second character has a strictly greater attack and defense.

Constraints:

- `2 <= properties.length <= 105`
- `properties[i].length == 2`
- `1 <= attacki, defensei <= 105`