Score : 400 points
On a two-dimensional plane, there are N red points and N blue points. The coordinates of the i-th red point are (a_i, b_i), and the coordinates of the i-th blue point are (c_i, d_i).
A red point and a blue point can form a friendly pair when, the x-coordinate of the red point is smaller than that of the blue point, and the y-coordinate of the red point is also smaller than that of the blue point.
At most how many friendly pairs can you form? Note that a point cannot belong to multiple pairs.
Input is given from Standard Input in the following format:
N a_1 b_1 a_2 b_2 : a_N b_N c_1 d_1 c_2 d_2 : c_N d_N
Print the maximum number of friendly pairs.
3 2 0 3 1 1 3 4 2 0 4 5 5
2
For example, you can pair (2, 0) and (4, 2), then (3, 1) and (5, 5).
3 0 0 1 1 5 2 2 3 3 4 4 5
2
For example, you can pair (0, 0) and (2, 3), then (1, 1) and (3, 4).
2 2 2 3 3 0 0 1 1
0
It is possible that no pair can be formed.
5 0 0 7 3 2 2 4 8 1 6 8 5 6 9 5 4 9 1 3 7
5
5 0 0 1 1 5 5 6 6 7 7 2 2 3 3 4 4 8 8 9 9
4