#include <algorithm>
#include <bits/stdc++.h>
using namespace std;

int main() {
	int n;
    cin >> n;
    vector<pair<int, int>> v(n);
    map<int, int> napok;
    for(int i = 0; i < n; i++) cin >> v[i].second >> v[i].first;
    sort(v.begin(), v.end());
    //for(auto i : v) cout << i.second << " " << i.first << endl;
    int cnt = n;
    for(int i = 0; i < n; i++) {
        if(napok[v[i].second] > 0) {
            napok[v[i].second]--;
            cnt--;
        }
        napok[v[i].first]++;
    }
    cout << cnt << endl;
}
// 2 3  3 100  100 200  200 300
// 2 3
// 100 101