import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main
{
    private static int N=1010;
    private static List<Integer>[] g1=new ArrayList[N];//java中邻接表
    private static List<Integer>[] g2=new ArrayList[N];
    private static boolean[] st1=new boolean[N];
    private static boolean[] st2=new boolean[N];
    private static int n,m;

    public static void main(String[] args)
    {
        Scanner scan=new Scanner(System.in);

        n=scan.nextInt();
        m=scan.nextInt();

        for(int i=1;i<=n;i++)
            g1[i]=new ArrayList<>();
        for(int i=1;i<=n;i++)
            g2[i]=new ArrayList<>();

        while(m--!=0)
        {
            int a=scan.nextInt();
            int b=scan.nextInt();
            g1[a].add(b);
            g2[b].add(a);
        }

        int res=0;
        for(int i=1;i<=n;i++)
        {
            for(int j=1;j<=n;j++)
            {
                st1[j]=false;
                st2[j]=false;
            }

            dfs(i,g1,st1);
            dfs(i,g2,st2);

            int cnt=0;
            for(int j=1;j<=n;j++)
                if(st1[j]||st2[j])
                    cnt++;
            if(cnt==n)
                res++;
        }
        System.out.println(res);

        scan.close();

    }

    private static void dfs(int u, List<Integer>[] g, boolean[] st)
    {
        st[u]=true;
        for(int i=0;i<g[u].size();i++)
        {
            int t=g[u].get(i);
            if(!st[t])
                dfs(t,g,st);
        }

    }

}