#include <fstream>
#include <vector>
#define DIM 100001
using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");
int n, m, x, y, cnt;
bool viz[DIM];
vector<int> a[DIM];

void dfs(int nod) {
	viz[nod] = true;
	for (int i = 0; i < a[nod].size(); i++)
		dfs(a[nod][i]);
}

int main() {
	fin >> n >> m;
	while (m--) {
		fin >> x >> y;
		a[x].push_back(y);
	}
	for (int i = 0; i < n; i++)
		if (!viz[i]) {
			dfs(i);
			cnt++;
		}
	fout << cnt;
	return 0;
}