#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;

inline int next_int() {
	int d;
	scanf("%d", &d);
	return d;
}

const int V = 100000;
const int E = 200000;

int ec, eb[V], en[E], et[E], seen[V];

int dfs(int u) {
	if (seen[u]) {
		return 0;
	}
	seen[u] = true;
	int n = 1;
	for (int e = eb[u]; e != -1; e = en[e]) {
		int v = et[e];
		n += dfs(v);
	}
	return n;
}

int main() {
	freopen("dfs.in", "r", stdin);
	freopen("dfs.out", "w", stdout);
	memset(eb, -1, sizeof eb);
	int n = next_int();
	int m = next_int();
	for (int i = 0; i < m; i++) {
		int u = next_int() - 1;
		int v = next_int() - 1;
		et[ec] = v;
		en[ec] = eb[u];
		eb[u] = ec++;
	}
	int ans = 0;
	for (int i = 0; i < n; i++) {
		if (dfs(i)) {
			ans++;
		}
	}
	printf("%d", ans);
	return 0;
}