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: Wrong Answer)

N = int(input())
AB = [list(map(int,input().split())) for i in range(N)]
CD = [list(map(int,input().split())) for i in range(N)]

AB.sort()
CD.sort()

#print(AB)
#print(CD)

li = [[] for i in range(N)]

for i in range(N):
    ab = AB[i]
    for j in range(N):
        cd = CD[j]
        if ab[0] < cd[0] and ab[1] < cd[1]:
            li[i].append(cd)

#print(li)

newli = []
for i in range(N):
    if li[i] != []:
        newli.append(li[i])
    else:
        N -= 1

li = newli

ans = 0
while len(li) != 0:
    l = 1000
    
    for i in range(N):
        l = min(l,len(li[i]))

    for i in range(N):
        if len(li[i]) == l:
            rem = li[i].pop()
            remli = li[i]
            ans += 1
            break

    for j in range(N):
        if rem in li[j]:
            li[j].remove(rem)

    newli = []
    for i in range(N):
        if li[i] != []:
            newli.append(li[i])
        else:
            N -= 1

    li = newli

print(ans)