#include <iostream>
#include <fstream>
#include <vector>
#define NMAX 100005
using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");
vector<vector<int>> gr;
int N, M;
bool d[NMAX];
void read() {
    int x, y;
    fin >> N >> M;
    gr.resize(N + 1);
    for (int i = 0; i < M; ++i) {
        fin >> x >> y;
        gr[x].push_back(y);
    }
}
void dfs(int node) {
    d[node] = true;
    for (auto x : gr[node]) {
        if (d[x] == false) {
            dfs(x);
        }
    }
}
int main()
{
    int con = 0;
    read();
    for (int i = 1; i <= N; ++i) {
        if (d[i] == false) {
            dfs(i);
            ++con;
        }
    }
    fout << con << "\n";
    return 0;
}