#include <iostream>
#include <vector>
#include <unordered_set>
#include <algorithm>
 
using namespace std;
 
// Function to select the maximum number of warriors
int maxWarriors(vector<pair<int, int>>& warriors, int N) {
    unordered_set<int> selectedNumbers; // Set to keep track of selected identification numbers
 
    for (int i = 0; i < N; ++i) {
        if (selectedNumbers.find(warriors[i].first) == selectedNumbers.end()) {
            // If Xi is not used yet, use it
            selectedNumbers.insert(warriors[i].first);
        } else if (selectedNumbers.find(warriors[i].second) == selectedNumbers.end()) {
            // If Xi is used but Yi is not used, use Yi
            selectedNumbers.insert(warriors[i].second);
        }
    }
 
    return selectedNumbers.size();
}
 
int main() {
    int N;
    cin >> N;
    vector<pair<int, int>> warriors(N);
 
    for (int i = 0; i < N; ++i) {
        cin >> warriors[i].first >> warriors[i].second;
    }
 
    int result = maxWarriors(warriors, N);
    cout << result << endl;
 
    return 0;
}