额额额，趋向向天歌。

#include<bits/stdc++.h>
using namespace std;
int n,m,ans;
vector<int> w[10010];
bool vis[10010];
queue<int> q;
bool bfs(int now){
    memset(vis,0,sizeof(vis));
    vis[now]=1;
    q.push(now);
    while(!q.empty()){
        int now=q.front();
        q.pop();
        for(register int i=0;i<w[now].size();i++){
            int t=w[now][i];
            if(!vis[t]){
                vis[t]=1;
                q.push(t);
            }
        }
    }
    for(register int i=1;i<=n;i++){
        if(!vis[i]) return 0;
    }
    return 1;
}
int main(){
    scanf("%d%d",&n,&m);
    while(m--){
        int x,y;
        scanf("%d%d",&x,&y);
        w[y].push_back(x);
    } 
    for(register int i=1;i<=n;i++){
       if(bfs(i)) ans++;
    }
    printf("%d",ans);
    return 0;
}