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++14 (GCC 5.4.1) (judge verdict: Runtime Error)

#include<bits/stdc++.h>
#define fi first
#define se second
#define show(x) cerr<<#x<<"="<<x<<"\n"
typedef long long ll;
using namespace std;
const ll inf=(ll)1e14;
int n;
vector<pair<int,int> > aka,ao;

struct edge
{
  int to;
  ll cap;
  int rev;
};
vector<edge> v[201];
int level[201];
int iter[201];

void add_edge(int from,int to,ll cost){
  v[from].push_back({to,cost,(int)v[to].size()});
  v[to].push_back({from,0,(int)v[from].size()-1});
}

void bfs(int s){
  memset(level,-1,sizeof(level));
  queue<int> q;
  q.push(s);
  level[s]=0;
  while(!q.empty()){
    int now=q.front();
    q.pop();
    for(int i=0;i<(int)v[now].size();i++){
      if(v[now][i].cap>0 && level[v[now][i].to]<0){
        level[v[now][i].to]=level[now]+1;
        q.push(v[now][i].to);
      }
    }
  }
}

int dfs(int now,int t,ll f){
  if(now==t)return f;
  for(int &i=iter[now];i<(int)v[now].size();i++){
    if(v[now][i].cap>0 && level[now]<level[v[now][i].to]){
      int d=dfs(v[now][i].to,t,min(f,v[now][i].cap));
      if(d>0){
        v[now][i].cap-=d;
        v[v[now][i].to][v[now][i].rev].cap+=d;
        return d;
      }
    }
  }
  return 0;
}

int max_flow(int s,int t){
  int flow=0;
  for(;;){
    bfs(s);
    if(level[t]<0)return flow;
    memset(iter,0,sizeof(iter));
    int f;
    while((f=dfs(s,t,inf))>0){
      flow+=f;
    }
  }
}

int main(){
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.precision(10);
  cout<<fixed;
#ifdef LOCAL_DEFINE
  FILE *stream1;
  //FILE *stream2;
  stream1=freopen("in","r",stdin);
  //stream2=freopen("out","w",stdout);
  if(stream1==NULL)return 0;
  //if(stream2==NULL)return 0;
#endif
  cin>>n;
  int s=2*n;
  int t=s+1;
  for(int i=0;i<n;i++){
    int a,b;cin>>a>>b;
    aka.push_back({a,b});
    add_edge(s,i,1);
  }
  for(int i=0;i<n;i++){
    int a,b;cin>>a>>b;
    add_edge(n+i,t,1);
    ao.push_back({a,b});
  }
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      if(aka[j].fi<ao[i].fi && aka[j].se<ao[i].se){
        add_edge(j,n+i,1);
      }
    }
  }
  cout<<max_flow(s,t)<<endl;
  /*
  cin>>n;
  for(int i=0;i<n;i++){
    int a,b;cin>>a>>b;
    aka.push_back({a,b});
  }
  for(int i=0;i<n;i++){
    int a,b;cin>>a>>b;
    ao.push_back({a,b});
  }
  sort(ao.begin(),ao.end());
  int ans=0;
  for(int i=0;i<n;i++){
    int maxy=-1;
    int res=-1;
    for(int j=0;j<n;j++){
      if(past[j])continue;
      if(aka[j].fi<ao[i].fi && aka[j].se<ao[i].se){
        if(maxy<aka[j].se){
          res=j;
          maxy=aka[j].se;
        }
      }
    }
    if(res!=-1){
      past[res]=1;
      ans++;
    }
  }
  print(ans);*/
#ifdef LOCAL_DEFINE
  cerr<<"Time elapsed: "<<1.0*clock()/CLOCKS_PER_SEC<<"s.\n";
  fclose(stream1);
  //fclose(stream2);
#endif
  return 0;
}