BAEKJOON 2458 DFS

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.StringTokenizer;

public class Main {
	static int N, M, cnt, ans;
	static ArrayList<Integer>[] big, small;
	static boolean[] visit;

	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer(br.readLine());
		N = Integer.parseInt(st.nextToken());
		M = Integer.parseInt(st.nextToken());
		big = new ArrayList[N + 1];
		small = new ArrayList[N + 1];
		for (int i = 1; i < N + 1; i++) {
			big[i] = new ArrayList<>();
			small[i] = new ArrayList<>();
		}
		for (int i = 0; i < M; i++) {
			st = new StringTokenizer(br.readLine());
			int s = Integer.parseInt(st.nextToken());
			int e = Integer.parseInt(st.nextToken());
			big[s].add(e);
			small[e].add(s);
		}
		for (int i = 1; i < N + 1; i++) {
			visit = new boolean[N + 1];
			cnt = 0;
			dfsbig(i);
			dfssmall(i);
			if (cnt == N - 1)
				ans++;
		}
		System.out.println(ans);
	}

	private static void dfsbig(int n) {
		visit[n] = true;
		for (int b : big[n]) {
			if (!visit[b]) {
				cnt++;
				dfsbig(b);
			}

		}
	}

	private static void dfssmall(int n) {
		visit[n] = true;
		for (int s : small[n]) {
			if (!visit[s]) {
				cnt++;
				dfssmall(s);
			}
		}
	}
}