#include<iostream>
#include<vector>
#include<stack>
using namespace std;
const int N=10010;
vector<int> g[N];
stack<int>s;
bool vis[N];
int dfn[N],low[N],scc[N],sccnum,cnt,sizze[N];
void tarjan(int u)
{
    int v;
    dfn[u]=low[u]=++cnt;
    s.push(u);
    vis[u]=true;
    for(int i=0;i<g[u].size();i++)
    {
        v=g[u][i];
        if(!dfn[v])
        {
            tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        else low[u]=min(low[u],dfn[v]);
    }
    if(low[u]==dfn[u])
    {
        cnt++;
        do
        {
            v=s.top();
            s.pop();
            vis[v]=false;
            scc[v]=cnt;
            sizze[cnt]++;
            
        } while (v!=u);
        
    }
}
int main()
{
    int n,m,u,v,i,j;
    scanf("%d%d",&n,&m);
    for(i=1;i<=m;i++)
    {
        scanf("%d%d",&u,&v);
        g[u].push_back(v);
    }
    for(i=1;i<=n;i++)
        if(dfn[i]==0)
            tarjan(i);
    int res=0;
    for(i=1;i<=cnt;i++)
        if(sizze[i]>1) res++;
    printf("%d",res);
    return 0;
}