#include<cstdio>
#include<cstdlib>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<ctime>
using namespace std;
const int N=50005;
int n,m,head[N],dfs[N],stack[N],low[N],cnt,t,top,ans;
bool vis[N];
struct node{
int u,v,next;
}edge[N];
void push(int u,int v){
++cnt;
edge[cnt].u=u;
edge[cnt].v=v;
edge[cnt].next=head[u];
head[u]=cnt;
}
void tarjan(int u){
dfs[u]=low[u]=++t;
stack[++top]=u;
vis[stack[top]]=1;
for(int i=head[u];i!=-1;i=edge[i].next){
if(!dfs[edge[i].v]){
tarjan(edge[i].v);
}
if(vis[edge[i].v]){
low[u]=min(low[u],low[edge[i].v]);
}
}
if(low[u]==dfs[u]){
for(++ans;stack[top+1]!=u;){
vis[stack[top--]]=0;
}
}
}
int main(){
int u,v;
scanf("%d%d",&n,&m);
memset(head,-1,sizeof(head));
for(int i=1;i<=m;i++){
scanf("%d%d",&u,&v);
push(u,v);
}
for(int i=1;i<=n;i++){
if(!dfs[i]){
tarjan(i);
}
}
printf("%d\n",ans);
system("pause");
return 0;
}