#include<bits/stdc++.h>
using namespace std;
struct eg{
    int t,f,n;
}e[200100];
int n,m,hd[100100],cnt=0,rd[100100]={0},cd[100100],ans=0,rd2[100100]={0};
int sum[100100]={0};
void add(int x,int y){
    e[++cnt].f=x;
    e[cnt].t=y;
    e[cnt].n=hd[x];
    hd[x]=cnt;
}
void bfs(){
    queue<int>q;
    for(int i=1;i<=n;i++){
        if(rd[i]==0)q.push(i),sum[i]=1;
    }
    while(!q.empty()){
        int u=q.front();q.pop();
        for(int i=hd[u];i;i=e[i].n){
            int ver=e[i].t;
            sum[ver]=sum[ver]+sum[u];
            rd[ver]--;
            if(rd[ver]==0){
                q.push(ver);
            }
        }
    }
}
int main(){
    freopen("chain_2016.in","r",stdin);
    freopen("chain_2016.out","w",stdout);
    cin>>n>>m;
    for(int i=1;i<=m;i++){
        int a,b;
        cin>>a>>b;
        rd[b]++;cd[a]++;
        rd2[b]++;
        add(a,b);
    }
    bfs();
    for(int i=1;i<=n;i++){
        if(cd[i]==0&&rd2[i]!=0)ans+=sum[i];
    }
    cout<<ans<<endl;
    return 0;
}