Problem:
Score : 400 points

Problem Statement

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.

Constraints

All input values are integers.

1 \leq N \leq 100

0 \leq a_i, b_i, c_i, d_i < 2N

a_1, a_2, ..., a_N, c_1, c_2, ..., c_N are all different.

b_1, b_2, ..., b_N, d_1, d_2, ..., d_N are all different.

Input

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

Output

Print the maximum number of friendly pairs.

Sample Input 1

3
2 0
3 1
1 3
4 2
0 4
5 5

Sample Output 1

2

For example, you can pair (2, 0) and (4, 2), then (3, 1) and (5, 5).

Sample Input 2

3
0 0
1 1
5 2
2 3
3 4
4 5

Sample Output 2

2

For example, you can pair (0, 0) and (2, 3), then (1, 1) and (3, 4).

Sample Input 3

2
2 2
3 3
0 0
1 1

Sample Output 3

0

It is possible that no pair can be formed.

Sample Input 4

5
0 0
7 3
2 2
4 8
1 6
8 5
6 9
5 4
9 1
3 7

Sample Output 4

5

Sample Input 5

5
0 0
1 1
5 5
6 6
7 7
2 2
3 3
4 4
8 8
9 9

Sample Output 5

4

Solution in Python (3.4.3) (judge verdict: Accepted)

dat_r = []
dat_b = []

n = int(input())
for i in range(n):
    a,b = map(int, input().split())
    dat_r.append((a, b))

for i in range(n):
    c,d = map(int, input().split())
    dat_b.append((c, d))

dat_r.sort(key=lambda x: ( -x[1], -x[0]-x[1]))
dat_b.sort(key=lambda x: ( +x[0],  x[0]+x[1]))
#print("")
#print(dat_r)
#print(dat_b)
res = 0
"""
for i in range(n):
    for j in range(len(dat_b)):
        # print("{0} < {1} vs {2} < {3}".format(dat_r[i][0] ,dat_b[j][0] ,dat_r[i][1] ,dat_b[j][1]))
        if dat_r[i][0] < dat_b[j][0] and dat_r[i][1] < dat_b[j][1]:
            # print("ok")
            res += 1
            dat_b  = dat_b[0:j] + dat_b[j + 1:]
            break
print(res)
"""
for i in range(n):
    for j in range(len(dat_r)):
        #print("{0} < {1} vs {2} < {3}".format(dat_r[i][0] ,dat_b[j][0] ,dat_r[i][1] ,dat_b[j][1]))
        if dat_r[j][0] < dat_b[i][0] and dat_r[j][1] < dat_b[i][1]:
            #print("ok")
            res += 1
            dat_r  = dat_r[0:j] + dat_r[j + 1:]
            break
print(res)