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, cd = [], []
for _ in range(N):
    a_, b_ = list(map(int, input().split()))
    ab.append([a_, b_])
for _ in range(N):
    c_, d_ = list(map(int, input().split()))
    cd.append([c_, d_])

v = [[0 for i in range(N)] for _ in range(N)]
vsum = [[0, i] for i in range(N)]

for i, x in enumerate(ab):
    for j, y in enumerate(cd):
        if (x[0] < y[0]) & (x[1] < y[1]):
            v[i][j] = 1
            vsum[i][0] += 1
vsum.sort()
ans = 0
for x, i in vsum:
    vvv = v[i]
    crit = []
    for j, v4 in enumerate(vvv):
        t = 0
        if v4 == 1:
            for k in range(N):
                if v[k][j] == 1:
                    t += 1
            crit.append([t, j])
    if len(crit) > 0:
        crit.sort()
        zero_i = crit[0][1]
        for k in range(N):
            v[k][zero_i] = 0
        ans += 1
print(ans)