#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<algorithm>
#include<ctime>
using namespace std;
const int N=10005;
int n,m,cnt,rcnt,head[N],rhead[N],t,rt,ans;
bool vis[N],rvis[N];
struct Node{
    int u,v,next;
}edge[N];
struct rNode{
    int u,v,next;
}redge[N];
struct Node1{
    int id,val;
}f[N];
bool cmp(Node1 p,Node1 q){
    return p.val>q.val;
}
void push(int u,int v){
    ++cnt;
    edge[cnt].u=u;
    edge[cnt].v=v;
    edge[cnt].next=head[u];
    head[u]=cnt;
}
void rpush(int u,int v){
    ++rcnt;
    redge[rcnt].u=u;
    redge[rcnt].v=v;
    redge[rcnt].next=rhead[u];
    rhead[u]=rcnt;
}
void kosaraju(int u){
    vis[u]=true;
    for(int i=head[u];i!=-1;i=edge[i].next){
        int v=edge[i].v;
        if(!vis[v]){
            kosaraju(v);
        }
    }
    f[u].val=++rt;
}
void rkosaraju(int u){
    vis[u]=true;
    for(int i=rhead[u];i!=-1;i=redge[i].next){
        int v=redge[i].v;
        if(!vis[v]){
            rkosaraju(v);
        }
    }
}
int main(){
    memset(head,-1,sizeof(head));
    memset(rhead,-1,sizeof(rhead));
    memset(vis,false,sizeof(vis));
    int u,v;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++){
        scanf("%d%d",&u,&v);
        push(u,v);
        rpush(v,u);
    }
    for(int i=1;i<=n;i++){
        f[i].id=i;
        if(!vis[i]){
            kosaraju(i);
        }
    }
    memset(vis,false,sizeof(vis));
    sort(f+1,f+1+n,cmp);
    for(int i=1;i<=n;i++){
        if(!vis[f[i].id]){
            rkosaraju(f[i].id);
            ++ans;
        }
    }
    printf("%d",ans);
    return 0;
}