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 C++ (GCC 9.2.1) (judge verdict: Accepted)

//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i=a;i<b;i++)
#define rep(i,n) FOR(i,0,n)
#define ROF(i,a,b) for(int i=a;i>=b;i--)
#define per(i,a) ROF(i,a,0)
#define pb push_back
using namespace std;
using ll=long long;
using ld=long double;
typedef pair<ll,ll> P;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<P> vP;
typedef vector<char> vc;
typedef vector<vc> vvc;
const ll MOD=1000000007;
const ll MOD2=998244353;
const ld PI=acos(-1);
const ll INF=1e18;
struct edge{ll to,cost;};
struct edge2{ll from,to,cost;};

template <typename T>
bool chmax(T &a, const T& b) {
    if (a < b) {
      a = b;
        return true;
    }
    return false;
}

template <typename T>
bool chmin(T &a, const T& b) {
    if (a > b) {
      a = b;
      return true;
    }
    return false;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int N;
    cin >> N;
    vP p(N),q(N);
    rep(i,N){
        cin >> p[i].first >> p[i].second;
    }
    rep(i,N){
        cin >> q[i].first >> q[i].second;
    }
    sort(p.begin(),p.end(),greater<P>());
    sort(q.begin(),q.end(),greater<P>());
    set<int> st;
    st.insert(1e9);
    ll ans=0;
    ll np=0,nq=0;
    per(i,2*N-1){
        if(nq!=N&&q[nq].first==i){
            st.insert(q[nq].second);
            nq++;
        }
        if(np!=N&&p[np].first==i){
            int z=*st.lower_bound(p[np].second+1);
            if(z!=1e9){
                ans++;
                st.erase(z);
            }
            np++;
        }
    }
    cout << ans << endl;cerr<< 1 << endl;
}
/*
overflow checked?
corner case checked?
boundary checked?
not TLE in worst case checked?
*/