#include <iostream>
#include <map>
#include <vector>
#include <algorithm>


using namespace std;

bool eszerint(pair<int, int> p1, pair<int, int> p2)
{
    if(p1.first==p2.first)
        return p1.second<p2.second;
    else
        return p1.first<p2.first;
}
int main()
{
    int n;
    cin>>n;
    vector<pair<int, int>> v(n);
    for(int i=0;i<n;i++)
        cin>>v.at(i).first>>v.at(i).second;

    map<int, int> k;
    int tot = n;
    for (int i = 0; i < n; i++)
     {
        if (k[v[i].first] > 0)
            {
            k[v[i].first]--;
            tot--;
        }
        k[v[i].second]++;
    }
    cout << tot << endl;

    return 0;
}