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

void DFS(int node, vector<int> adj[], vector<int> &color) {
    color[node] = 1;
    for(int i = 0; i < adj[node].size(); i++) {
        if(color[adj[node][i]] == 0) {
            DFS(adj[node][i], adj, color);
        }
    }
    color[node] = 2;
}

const int kNmax = 100005; 

int main() {
    int n;
	int m;
    int x,y;
	int source;
    vector<int> adj[kNmax];
    vector<int> color;
    ifstream fin("dfs.in");
	fin >> n >> m;
	for (int i = 1; i <= m; i++) {
		fin >> x >> y;
		adj[x].push_back(y);
	}
    color.push_back(-1);
    for(int i = 1; i<=n;i++){
        color.push_back(0);
    }
    int conex = 0;
    for(int i = 1; i <= n; i++) {
        if(color[i]==0){
            DFS(i, adj, color);
            conex++;
        }
    }
    ofstream fout("dfs.out");
    fout << conex;
    fout.close();
	fin.close();
}