#include <bits/stdc++.h>
/*
#include <algorithm>
#include <fstream>
#include <iostream>
#include <map>
#include <vector>
*/

/*
9
1 3
2 4
8 10
1 7
2 7
2 3
9 11
3 9
3 8
*/

using namespace std;
bool elobb(pair<int, int> x,  pair<int, int > y)
{
    if(x.second==y.second)
        return x.first<y.first;
    return  x.second<y.second;
}


int main()
{
    int N;
    vector<pair<int, int> > v;
    cin >> N;
    for (int i = 0; i < N; i++) {
        int a, b;
        cin >> a >> b;
        v.push_back({a, b});
    }

    sort(v.begin(), v.end(), elobb);
/*
    for(pair<int,int> x : v)
        cout<<x.first<<"--"<<x.second<<endl;
    cout<<endl;
*/
    map<int, int> k;
    int tot = N;  //kezdetben N nap

    //for(int i=0;i<N;i++)
      // cout<<k[v[i].first]<<" "<<k[v[i].second]<<endl;

    for (int i = 0; i < N; i++)
    {
  //      cout<<i<<"***"<<tot<<" "<<k[v[i].first]<<" "<<k[v[i].second];
        if (k[v[i].first] > 0)
        {
            k[v[i].first]--;

            tot--;

        }
        k[v[i].second]++;
    //    cout<<"-->"<<k[v[i].first]<<" "<<k[v[i].second]<<endl;

    }
    cout << tot << endl;
}