#include<bits/stdc++.h>
using namespace std;
const int maxn = 1e4 + 10, maxm = 5e4 + 10, Inf = 0x3f3f3f3f;
int d[maxn], head[maxn], repeat[maxn][maxn];
int len, n, m, ans;
int read() {
	int f = 1, k = 0;
	char c = getchar();
	while (c < '0' || c > '9') {
		c = getchar();
	}
	while (c >= '0' && c <= '9') {
		k = k * 10 + (c ^ 48);
		c = getchar();
	}
	return f * k;
}
struct Edge {
	int from, to, nxt, w;
} e[maxm];
void add(int u, int v, int w) {
	e[++len].from = u;
	e[len].to = v;
	e[len].w = w;
	e[len].nxt = head[u];
	head[u] = len;
}
struct Node {
	int num, dis;
	Node(int x, int y) {
		num = x;
		dis = y;
	}
};
bool operator <(const Node &a, const Node &b) {
	return a.dis > b.dis;
}
void dij(int s) {
	priority_queue<Node>q;
	memset(d, Inf, sizeof d);
	q.push(Node(s, 0));
	d[s] = 0;
	while (!q.empty()) {
		int u = q.top().num;
		q.pop();
		for (int i = head[u]; i; i = e[i].nxt) {
			int v = e[i].to;
			if (d[v] > d[u] + e[i].w) {
				d[v] = d[u] + e[i].w;
				q.push(Node(v, d[v]));
			}
		}
	}
}
bool solv() {
	for (int i = 1; i <= n; ++i) {
		if (d[i] == Inf) {
			return 1;
		}
	}
	return 0;
}
int main() {
	n = read(), m = read();
	int a, b;
	for (int i = 1; i <= m; ++i) {
		a = read(), b = read();
		if (repeat[b][a] == 0) {
			add(b, a, 1);
			repeat[b][a]++;
		}
	}
	for (int i = 1; i <= n; ++i) {
		if (repeat[b][a] == 1) {
			dij(i);
			if (!solv()) {
				ans++;
			}
		}
	}
	printf("%d", ans);
	return 0;
}