// KKGyak.cpp : This file contains the 'main' function. Program execution begins and ends there.
//
using namespace std;

#include <iostream>
#include <map>
#include <set>
#include <unordered_set>

int main()
{
    int a;
    cin >> a;
	map<int, multiset<int>> dataStr;
	unordered_set<int> exists;
	for (size_t i = 0; i < a; i++)
	{
		int a, b;
		cin >> a >> b;
		if (exists.count(a) == 0) {
			dataStr.insert({ a,multiset<int>() });
			exists.insert(a);
		}
		dataStr[a].insert(b);
	}
	int res = 0;
	while (true)
	{
		int chain = -1;
		for (auto m : dataStr) {
			if (m.second.size() > 0) {
				chain = *m.second.begin();
				dataStr[m.first].erase(dataStr[m.first].begin());
				break;
			}
		}
		if (chain == -1) break;
		while (true)
		{
			if (exists.count(chain) == 1 && dataStr[chain].size()>0) {
				int old = chain;
				chain = *dataStr[chain].begin();
				dataStr[old].erase(dataStr[old].begin());
			}
			else break;
		}
		res++;
	}
	cout << res;
}

// Run program: Ctrl + F5 or Debug > Start Without Debugging menu
// Debug program: F5 or Debug > Start Debugging menu

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//   1. Use the Solution Explorer window to add/manage files
//   2. Use the Team Explorer window to connect to source control
//   3. Use the Output window to see build output and other messages
//   4. Use the Error List window to view errors
//   5. Go to Project > Add New Item to create new code files, or Project > Add Existing Item to add existing code files to the project
//   6. In the future, to open this project again, go to File > Open > Project and select the .sln file