#include <bits/stdc++.h>

using namespace std;

const int N = (int) 1e5 + 7;
int n, m, src, d[N];
vector<int> g[N];

int main() {
#ifdef INFOARENA
	freopen ("dfs.in", "r", stdin);
	freopen ("dfs.out", "w", stdout);
#endif

	cin >> n >> m;
	for (int i = 1; i <= m; i++) {
		int a, b;
		cin >> a >> b;
		g[a].push_back(b);
	}
	for (int i = 1; i <= n; i++) {
		d[i] = -1;
	}
	vector<int> q;
	int comps = 0;
	for (int src = 1; src <= n; src++) {
		if (d[src] != -1) {
			continue;
		}
		comps++;
		q.clear();
		q.push_back(src);
		d[src] = 0;
		for (int it = 0; it < (int) q.size(); it++) {
			int a = q[it];
			for (auto &b : g[a]) {
				if (d[b] == -1) {
					d[b] = 1 + d[a];
					q.push_back(b);
				}
			}
		}
	}
	cout << comps << "\n";
	return 0;
}