import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;
import java.util.stream.IntStream;

public class StronglyConnected {
    private static int numberOfStronglyConnectedComponents(ArrayList<Integer>[] adj) {
        ArrayList<Integer>[] adjReversa1 = reverseG(adj);
        boolean[] adjReversalVisited = new boolean[adj.length];
        int[] postV = new int[adj.length];
        int[] clock = new int[1];
        dfs(adjReversa1, adjReversalVisited, postV, clock);

        // https://stackoverflow.com/questions/951848/java-array-sort-quick-way-to-get-a-sorted-list-of-indices-of-an-array/35701049
        int[] temp = IntStream.range(0, postV.length).boxed().sorted((i, j) -> postV[i] - postV[j]).mapToInt(ele -> ele).toArray();

        boolean[] visited = new boolean[adj.length];
        int sccCount = 0;


        for (int i = adj.length - 1; i > -1; i--) {
            if (!visited[temp[i]]) {
                exploreWithoutPostV(temp[i], adj, visited);
                sccCount++;
            }
        }
        return sccCount;
    }

    private static void dfs(ArrayList<Integer>[] adj, boolean[] visited, int[] postV, int[] clock) {
        for (int v = 0; v < adj.length; v++) {
            if (!visited[v])
                explore(v, adj, visited, postV, clock);
        }
    }

    private static void explore(int v, ArrayList<Integer>[] adj, boolean[] visited, int[] postV, int[] clock) {
        visited[v] = true;
        for (int w : adj[v]) {
            if (!visited[w])
                explore(w, adj, visited, postV, clock);
        }
        postV[v] = clock[0];
        clock[0] = clock[0] + 1;
    }

    private static void exploreWithoutPostV(int v, ArrayList<Integer>[] adj, boolean[] visited) {
        visited[v] = true;
        for (int w : adj[v]) {
            if (!visited[w])
                exploreWithoutPostV(w, adj, visited );
        }
    }


    private static ArrayList<Integer>[] reverseG(ArrayList<Integer>[] adj) {
        ArrayList<Integer>[] adjReverse = (ArrayList<Integer>[])new ArrayList[adj.length];
        for (int i = 0; i < adj.length; i++) {
            adjReverse[i] = new ArrayList<Integer>();
        }

        for (int v = 0; v < adj.length; v++) {
            for (int w : adj[v]) {
                adjReverse[w].add(v);
            }
        }
        return adjReverse;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int m = scanner.nextInt();
        ArrayList<Integer>[] adj = (ArrayList<Integer>[])new ArrayList[n];
        for (int i = 0; i < n; i++) {
            adj[i] = new ArrayList<Integer>();
        }
        for (int i = 0; i < m; i++) {
            int x, y;
            x = scanner.nextInt();
            y = scanner.nextInt();
            adj[x - 1].add(y - 1);
        }
        System.out.println(numberOfStronglyConnectedComponents(adj));
    }
}