You are given a 2D array of integers `envelopes` where `envelopes[i] = [w_i, h_i]` represents the width and the height of an envelope.
One envelope can fit into another if and only if both the width and height of one envelope are **strictly greater** than the width and height of the other.
Return the maximum number of envelopes you can Russian doll (i.e., put one inside the other).
**Note:** You cannot rotate an envelope.
Example 1
Input:envelopes = [[5,4],[6,4],[6,7],[2,3]]
Output:3
Explanation:The maximum number of envelopes you can Russian doll is 3 ([2,3] → [5,4] → [6,7]).