#include <iostream>
#include <vector>
#include <fstream>
#include <queue>
using namespace std;

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

class graf{
    int nrN;
    int nrM;
    vector<vector<int>> matriceAd;

public:
    graf(int n, int m, vector<vector<int>> &mat){
        nrN = n;
        nrM = m;
        matriceAd = mat;
    }

    void citire()
    {
        for (int i = 0; i < nrM; ++i){
            int x, y;
            fin >> x >> y;
            matriceAd[x].push_back(y);
        }
    }

    void BFS(int S){
        queue<int> coada;
        int x, y;
        vector<int> cost(nrN+1,-1);
        cost[S] = 0;
        coada.push(S);
        while ( !coada.empty() ){
            x = coada.front();
            coada.pop();
            for ( int i = 0; i < matriceAd[x].size(); ++i)
                if ( cost[matriceAd[x][i]] == -1 ){
                    cost[matriceAd[x][i]] = cost[x] + 1;
                    coada.push(matriceAd[x][i]);
                }
        }
        for ( int i = 0; i < nrN; i++ )
            fout << cost[i] << " ";
    }

    void DFS(){
        queue<int> coada;
        vector<int> viz(nrN + 1, 0);
        int it = 0;
        for (int i = 1; i <= nrN; ++i) {
            if (viz[i] == 0){
                int itaux = -1;
                it++;
                coada.push(i);
                while (!coada.empty()){
                    int x = coada.front();
                    viz[x] = it;
                    coada.pop();
                    for ( int j = 1; j < matriceAd[x].size(); ++j) {
                        if (matriceAd[x][j] != -1 && viz[matriceAd[x][j]] == 0)
                            coada.push(matriceAd[x][j]);
                        else if (viz[matriceAd[x][j]] != 0 && viz[matriceAd[x][j]] != it){
                            itaux = viz[matriceAd[x][j]];
                        }
                    }
                    if (itaux != -1) {
                        for (int k = 0; k < nrN; ++k) {
                            if (viz[k] == it)
                                viz[k] = itaux;
                        }
                        while (!coada.empty()) {
                            coada.pop();
                            it--;
                            break;
                        }
                    }
                }
            }
        }
        fout<<it;
    }
};
///BFS
//int main(){
//    int n, m, S;
//    fin >> n >> m >> S;
//    vector<vector<int>> mat;
//    vector<int> aux(1,-1);
//    mat.resize(n+1, aux);
//    graf G(n, m, mat);
//    G.citire();
//    G.BFS(S);
//
//    return 0;
//}

///DFS
int main(){
    int n, m;
    fin>>n>>m;
    vector<vector<int>> mat;
    vector<int> aux(1,-1);
    mat.resize(n+1, aux);
    graf G(n, m, mat);
    G.citire();
    G.DFS();
    return 0;
}