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


using namespace std;

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

const int NMAX = 100005;
const int MMAX = 1000005;

vector < int > G[NMAX];


int N, M, S;
int viz[NMAX];


queue < int > q;
void read() {
    fin >> N >> M;
    for (int i = 1; i <= M; i++) {
        int x, y;
        fin >> x >> y;
        G[x].push_back(y);
    }
}

void dfs(int nod) {
    viz[nod] = 1;
    for (int i = 0; i < G[nod].size(); i++) {
        int vecin = G[nod][i];
        if (viz[vecin] == 0)
            dfs(vecin);
    }
}


int main()
{
    int cc = 0;
    read();
    for (int i = 1; i <= N; i++) {
        if (viz[i] == 0) {
            cc++;
            dfs(i);
        }
    }
    cout << cc;
    return 0;
}