#include <iostream>
#include <cstdio>
#include <iomanip>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <bitset>
#include <stack>
#include <utility>
#include <numeric>
#include <algorithm>
#include <functional>
#include <cctype>
#include <complex>
#include <string>
#include <sstream>
#include <cassert>
using namespace std;

//common
typedef int  i32;
typedef long long i64,ll;
#define BR "\n"

#define ALL(c) (c).begin(),(c).end()
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define EACH(it,o) for(auto it = (o).begin(); it != (o).end(); ++it)
#define IN(l,v,r) ((l)<=(v) && (v)<(r))

typedef vector<int> vi; typedef pair<int,int> pii; typedef vector<pair<int,int> > vpii;
typedef long long ll; typedef vector<long long> vl; typedef pair<long long,long long> pll; typedef vector<pair<long long,long long> > vpll;
typedef vector<string> vs; typedef long double ld;

//config
#define MODE_DEBUG
//#define INF 1<<30
//#define EPS 1e-8
//const ll MOD =100000007;

//debug
#ifdef NDEBUG
#define DUMP(x)
#define DUMPLN(x)
#define DEBUG(x)
#define DEBUGLN(x)
#define LINE()
#define LINELN()
#define CHECK(exp,act)
#define STOP(e)
#else
#define DUMP(x)  cerr << #x << " = " << (x)
#define DUMPLN(x)  DUMP(x) <<endl
#define DEBUG(x) DUMP(x) << LINE() << " " << __FILE__
#define DEBUGLN(x) DEBUG(x)<<endl
#define LINE()    cerr<< " (L" << __LINE__ << ")"
#define LINELN()    LINE()<<endl
#define CHECK(exp,act)  if(exp!=act){DUMPLN(exp);DEBUGLN(act);}
#define STOP(e)  CHECK(e,true);if(!(e)) exit(1);
#endif

template<class T> inline string toString(const vector<T>& x) {
	stringstream ss;
	REP(i,x.size()){
		if(i!=0)ss<<" ";
		ss<< x[i];
	}
	return ss.str();
}
template<class T> inline string toString(const vector<vector<T> >& map) {
	stringstream ss;
	REP(i,map.size()){
		if(i!=0)ss<<BR;
		ss<< toString(map[i]);
	}
	return ss.str();
}
template<class K,class V>  string toString(map<K,V>& x) {
	string res;stringstream ss;
	for(auto& p:x)ss<< p.first<<":" << p.second<<" ";
	return ss.str();
}

template<typename T,typename V> inline T mod(T v,V MOD){
	return (v%MOD+MOD)%MOD;
}

#define nextInt(n) scanf("%d",&n)
#define nextLong(n) scanf("%lld",&n)
#define nextDouble(n) scanf("%lf",&n)

int INF=1<<28;

template<typename T>T gcd_positive(T a, T b) { return b == 0 ? a : gcd_positive(b,a%b); }
template<typename T>T gcd(T a, T b) { return gcd_positive(abs(a), abs(b)); }
template<typename T>T lcm(T a,T b){return a*b/gcd(a,b);}

namespace MaximamFlows{
    typedef int Flow;
    const int INF = 1 << 28;
    struct Edge{
        int to;Flow cap;int rev;
        Edge(int to,Flow cap,int rev) : to(to),cap(cap),rev(rev) {};
    };
    typedef vector<vector<Edge> > Graph;

    //dinic O(V^2*E)
    class MaximamFlow{
    private:
            //iter　次に調べる時の開始位置 距離
        vector<int> iter,dist;
            //sからのbfs距離の計算
        void bfs_dist(int s){
            fill(ALL(dist),-1);dist[s]=0;
            queue<int> que;que.push(s);
            while(!que.empty()){
                int v=que.front();que.pop();
                EACH(e,G[v]){
                    if(e->cap>0 && dist[e->to] == -1){
                        dist[e->to]=dist[v]+1;
                        que.push(e->to);
                    }
                }
            }
        }
            //増加パス
        Flow dfs_best_path(int v,int t,Flow f){
            if(v==t)return f;
            for(int &i =iter[v];i<(int)G[v].size();i++){
                Edge& e=G[v][i];
                if(e.cap>0 && dist[v]<dist[e.to]){
                    Flow d=dfs_best_path(e.to,t,min(f,e.cap));
                    if(d>0){
                        e.cap-=d;G[e.to][e.rev].cap+=d;
                        return d;
                    }
                }
            }
            return 0;
        }
    public:
        int V;Graph G;
        MaximamFlow(int V):V(V){
            G=Graph(V);
            dist=vector<int>(V);iter=vector<int>(V);
        }

        //ここがネックになるケースあり?
        void add_edge(int from,int to,int cap){
            int fromrev=G[to].size(),torev=G[from].size();
            G[from].push_back(Edge(to,cap,fromrev));G[to].push_back(Edge(from,0,torev));
        }
        int max_flow(int s,int t){
            Flow flow=0;
            while(true){
                bfs_dist(s);
                if(dist[t]<0)return flow;
                fill(ALL(iter),0);
                Flow f;
                while((f=dfs_best_path(s,t,INF))>0)flow+=f;
            }return -1;
        }
    };
}
using namespace MaximamFlows;


class Main{
public:	
	void run(){
		int N; cin >> N;
		vector<int> ws(N),hs(N);
		
		REP(i,N)cin >> ws[i] >> hs[i];
		
		MaximamFlow mf(2*N+2);
		REP(i,N)REP(j,N){
			if((min(ws[i],hs[i])< min(ws[j],hs[j])
				&& max(ws[i],hs[i])< max(ws[j],hs[j]))
			 )mf.add_edge(i,N+j,1);
		}
		REP(i,N)mf.add_edge(2*N,i,1);
		REP(i,N)mf.add_edge(N+i,2*N+1,1);
				
		cout << N-mf.max_flow(2*N,2*N+1)<<endl;
	}
};
 int main(){
 	cout <<fixed<<setprecision(15);
	ios::sync_with_stdio(false);
 	Main().run();
 	return 0;
 }


Measured memory_bytes: 1336