#include<iostream>

#include<cstdio>

#include<cstring>

#define maxn 10009

using namespace std;

int n,m,sumedge,top,sumclr,tim,ans;

int Stack[maxn],instack[maxn],low[maxn],dfn[maxn],cnt[maxn],head[maxn];

struct Edge{

    int x,y,nxt;

    Edge(int x=,int y=,int nxt=):

        x(x),y(y),nxt(nxt){}

}edge[maxn*];

void add(int x,int y){

    edge[++sumedge]=Edge(x,y,head[x]);

    head[x]=sumedge;

}

void Tarjian(int x){

    Stack[++top]=x;instack[x]=true;

    low[x]=dfn[x]=++tim;

    for(int i=head[x];i;i=edge[i].nxt){

        int v=edge[i].y;

        if(instack[v])low[x]=min(low[x],dfn[v]);

        else if(!dfn[v]){

            Tarjian(v);low[x]=min(low[x],low[v]);

        }

    }

    if(low[x]==dfn[x]){

        sumclr++;

        while(Stack[top+]!=x){

            instack[Stack[top]]=false;

            cnt[sumclr]++;

            top--;

        }

    }

}

int main(){

    scanf("%d%d",&n,&m);

    for(int i=;i<=m;i++){

        int x,y;

        scanf("%d%d",&x,&y);

        add(x,y);

    }

    for(int i=;i<=n;i++)if(!dfn[i])Tarjian(i);

    for(int i=;i<=sumclr;i++)if(cnt[i]>)ans++;

    printf("%d\n",ans);

    return ;

}