#include <stdio.h>

using namespace std;

#define MAX 200000

int lst[100000];
int urm[MAX],vf[MAX];
int nr,q[100000],viz[100000];
int p=1, u=0;

void adauga(int x,int y)
{
    vf[++nr]=y;
    urm[nr]=lst[x];
    lst[x]=nr;
}

void dfs(int x0)
{
    int x,poz,y;
    q[++u]=x0;
    while(p<=u)
    {
        x=q[p++];
        poz=lst[x];
        while(poz!=0)
        {
            y=vf[poz];
            if(viz[y]==0)
                viz[y]=1;
            poz=urm[poz];
        }
    }
}



int main()
{
    FILE *fin,*fout;

    fin=fopen("dfs.in","r");
    fout=fopen("dfs.out","w");

    int i,j,cnt,n,m,x,y;

    fscanf(fin,"%d%d",&n,&m);

    for(i=1;i<=m;i++)
    {
        fscanf(fin,"%d%d",&x,&y);
        adauga(x,y);
    }

    for(i=1;i<=n;i++)
    {
        if(viz[i]==0)
        {
            cnt++;
            dfs(i);
        }
    }

    fprintf(fout,"%d",cnt);

    return 0;
}