#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

ifstream f("dfs.in");
ofstream g("dfs.out");

vector <int> lv[100000];
vector <int>::iterator ii;

int main()
{
	int n, m, x, y;
	f >> n >> m;
	for (int i = 0; i < m; i++)
	{
		f >> x >> y;
		lv[x].push_back(y);
		//lv[y].push_back(x);
	}
	int nr = 0;
	for (int i = 1; i <= n; i++)
		for (ii = lv[i].begin(); ii != lv[i].end(); ++ii)
			nr++;
	g << n - nr;
	//cout << "\n";
	return 0;
}