#include<fstream>
#include<vector>
using namespace std;
fstream in("ctc.in");
ofstream out("ctc.out");
const int NMAX = 100005;

vector<int> G[NMAX],GT[NMAX],ctc[NMAX];
int N,M,post[NMAX],viz[NMAX],cnt;

void dfs(int nod)
{

    viz[nod] = 1;
    for(vector<int>::iterator it = G[nod].begin() ; it != G[nod].end() ; ++it)
        if(!viz[*it])
            dfs(*it);
    post[++cnt] = nod;
}

void dfs2(int nod,int sol)
{

    viz[nod] = 0;
    ctc[sol].push_back(nod);
    for(vector<int>::iterator it = GT[nod].begin() ; it != GT[nod].end() ; ++it)
        if(viz[*it])
            dfs2(*it,sol);
}

int main()
{

    int N,M;
    in>>N>>M;
    int x,y;
    for(int i = 1 ; i <= M ; ++i){

        in>>x>>y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }
    for(int i = 1 ; i <= N ; ++i)
        if(!viz[i])
            dfs(i);
    int sol = 0;
    for(int i = N ; i >= 1 ; --i)
        if(viz[post[i]]){
            ++sol;
            dfs2(post[i],sol);
        }
    out<<sol<<"\n";
    return 0;
}