#include <bits/stdc++.h>
using namespace std;
int n, m, t[100005], ans = 0, ans1[100005];
vector <int> a[100005];
queue <int> b;
void dfs(int x)
{
	if (a[x].size() == 0 && t[x] != 0)
	{
		ans++;
		return;
	}
	for (auto y : a[x])
		dfs(y);
}
int main()
{
	cin >> n >> m;
	for (int i = 1; i <= m; i++)
	{
		int xx, yy;
		cin >> xx >> yy;
		t[yy] ++;
		a[xx].push_back(yy);
	}
	for (int i = 1; i <= n; i++)
	{
		if (t[i] == 0)
			b.push(i);
	}
	while (b.size())
	{
		int xx = b.front();
		b.pop();
		dfs(xx);
	}
	cout << ans;
	return 0;
}

大佬们，dfs70分怎么优化啊