#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
using namespace std;
ifstream f("dfs.in");
ofstream g("dfs.out");
int n,s,k,st[100001],viz[100001],nr;
vector <vector<int> > a(100001);
void dfs(int x)
{
    st[1]=x;
    viz[x]=1;
    k=1;
    while(k>0)
    {
        int v=st[k];
int        y=0;
int ok=1;
        for(int i=0;i<a[v].size()&&ok;i++)
            if(viz[a[v][i]]==0)
        {
            y=a[v][i];
            ok=0;
        }
        if(y==0) k--;
        else
        {
            viz[y]=1;
            st[++k]=y;
        }
    }
}
int main()
{int m;
    f>>n>>m;
    for(int i=1;i<=m;i++)
    {
        int x,y;
        f>>x>>y;
        a[x].push_back(y);
    }
    for(int i=1;i<=n;i++)
    if(viz[i]==0) {nr++;dfs(i);}
    g<<nr;
    return 0;
}