#include <cstdio>

#define MAXN 100000
#define FOR(i,a,b) for(i=a;i<=b;i++)

using namespace std;

struct graf
{
    int nod;
    graf *next;
};

graf *a[MAXN];
int n,m,comp;
bool marked[MAXN];

inline void read()
{
    freopen("dfs.in","r",stdin);
    freopen("dfs.out","w",stdout);
    scanf("%d %d",&n,&m);
    int i;
    FOR(i,1,m)
    {
        int x,y;
        scanf("%d %d",&x,&y);
        graf *q=new graf;
        q->nod=y;
        q->next=a[x];
        a[x]=q;
    }
}

void dfs(int i)
{
    marked[i]=true;
    graf *q=a[i];
    while(q)
    {
        if(marked[q->nod]==false)
            dfs(q->nod);
        q=q->next;
    }
}


int main()
{
    int i;
    read();
    FOR(i,1,n)
    {
        if(marked[i]==false)
        {
            comp++;
            dfs(i);
        }
    }
    printf("%d\n",comp);
    return 0;
}