#include<iostream>

 #include<cstdio>

 #include<cstring>

 using namespace std;

 int min(int &a,int &b){return a<b?a:b;}

 #define N 10002

 #define M 50002

 int n,m,clo,dfn[N],low[N],blo,be[N],tp,st[N],ans;

 int cnt,hd[N],nxt[M<<],ed[N],poi[M<<];

 void adde(int x,int y){

     nxt[ed[x]]=++cnt; hd[x]=hd[x]?hd[x]:cnt;

     ed[x]=cnt; poi[cnt]=y;

 }

 void tarjan(int x){

     dfn[x]=low[x]=++clo; st[++tp]=x;

     for(int i=hd[x];i;i=nxt[i]){

         int to=poi[i];

         if(!dfn[to]){

             tarjan(to);

             low[x]=min(low[x],low[to]);

         }else if(!be[to]) low[x]=min(low[x],dfn[to]);

     }

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

         int tot=;

         be[x]=++blo;

         while(st[tp]!=x) be[st[tp--]]=blo,++tot;

         --tp; ans+=(tot>);

     }

 }

 int main(){

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

     for(int i=,q1,q2;i<=m;++i)

         scanf("%d%d",&q1,&q2),adde(q1,q2);

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

     printf("%d",ans);

     return ;

 }