#include <fstream>
#include <vector>

using namespace std; 

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

int v[100001];

void dfs(int s, vector< vector <int> > &g, int n){
	v[s] = 1;

	for(int i : g[s]){
		if(!v[i]){
			dfs(i, g, n);
		}
	}
}


int main(){
	int n, m, x, y, c=0;
	fin >> n >> m;

	vector< vector<int> > g(n+1);
	
	for(int i = 0; i < m; i++){
		fin >> x >> y;
		g[x].push_back(y);
	}

	for(int i = 1; i <= n; i++){
		if(!v[i]){
			dfs(i, g, n);
			c++;
		}
	}
	fout << c;	

	return 0;
}