#include <fstream>
#include <queue>
#include <vector>

using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");

int n,m,frec[50010],i,j,a,b,lung,nr;
vector<int> v[250010];
queue<int> coada;
int main()
{
    fin>>n>>m;
    for(i=1;i<=m;++i){
        fin>>a>>b;
        v[a].push_back(b);
    }
    for(i=1;i<=n;++i)
        if(!frec[i]){
            ++nr;
            frec[i]=nr;
            coada.push(i);
            while(!coada.empty()){
                a=coada.front();
                lung=v[a].size();
                for(j=0;j<lung;++j)
                    if(!frec[v[a][j]]){
                        frec[v[a][j]]=nr;
                        coada.push(j);
                    }
                coada.pop();
            }
        }
    fout<<nr;
    return 0;
}