import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Queue;

class Solution {
	public int solution(int n, int[][] results) {
		int answer = 0;

		HashMap<Integer, Athelete> map = new HashMap<Integer, Athelete>();
		/* 선수 객체 생성 */
		for (int i = 1; i <= n; i++) {
			ArrayList<Integer> left = new ArrayList<Integer>();
			ArrayList<Integer> right = new ArrayList<Integer>();
			Athelete athelete = new Athelete(i, left, right);
			map.put(i, athelete);
		}

		/* 운동선수 객체의 left, right 담아주기 */
		for (int i = 0; i < results.length; i++) {
			int winner = results[i][0];
			map.get(results[i][1]).left.add(winner);
			int loser = results[i][1];
			map.get(results[i][0]).right.add(loser);
		}

		/* BFS 탐색으로 왼쪽, 오른쪽 수 헤아리기 */
		for (int i = 1; i <= n; i++) {
			if (BFS(i, map) == n - 1) {
				answer++;
			}
		}
		return answer;
	}

	public int BFS(int id, HashMap<Integer, Athelete> map) {
		Athelete athelete = map.get(id);

		Queue<Athelete> leftQueue = new LinkedList<Athelete>();
		leftQueue.add(athelete);
		int total = 0;
		int[] leftVisitCheck = new int[map.size()];
		leftVisitCheck[id - 1] = 1;
        
		while (true) {
			if (leftQueue.isEmpty()) {
				break;
			}
			Athelete targetAthelete = leftQueue.poll();
			ArrayList<Integer> left = targetAthelete.left;

			for (int i = 0; i < left.size(); i++) {
				if (leftVisitCheck[left.get(i) - 1] == 1) {
					continue;
				}
				leftQueue.add(map.get(left.get(i)));
				leftVisitCheck[left.get(i) - 1] = 1;
				total++;
			}
		}

		Queue<Athelete> rightQueue = new LinkedList<Athelete>();
		rightQueue.add(athelete);
		int[] rightVisitCheck = new int[map.size()];
		rightVisitCheck[id - 1] = 1;
        
		while (true) {
			if (rightQueue.isEmpty()) {
				break;
			}
			Athelete targetAthelete = rightQueue.poll();
			ArrayList<Integer> right = targetAthelete.right;

			for (int i = 0; i < right.size(); i++) {
				if (rightVisitCheck[right.get(i) - 1] == 1) {
					continue;
				}
				rightQueue.add(map.get(right.get(i)));
				rightVisitCheck[right.get(i) - 1] = 1;

				total++;
			}
		}
		return total;
	}

}

class Athelete {
	int id;
	ArrayList<Integer> left;
	ArrayList<Integer> right;

	public Athelete(int id, ArrayList<Integer> left, ArrayList<Integer> right) {
		this.id = id;
		this.left = left;
		this.right = right;
	}
}