#include <bits/stdc++.h>
#include <unordered_map>
#define nmax 100006
#define MOD 1999999973
#define INF 2012345678
#define ll long long
using namespace std;
//#define fin cin
//#define fout cout

ifstream fin("dfs.in");
ofstream fout("dfs.out");

int n, m;
vector <int> L[nmax];
bitset <nmax> viz;

void DFS(int k)
{
	viz[k] = 1;
	for (int i : L[k])
		if (viz[i] == 0)
			DFS(i);
}

int main()
{
	int i, x, y, cnt;
	fin >> n >> m;
	for (i = 1; i <= m; i++)
	{
		fin >> x >> y;
		L[x].push_back(y);
	}
	
	cnt = 0;
	for (i = 1; i <= n; i++)
		if (viz[i] == 0)
		{
			DFS(i);
			cnt++;
		}
	
	fout << cnt << "\n";
	fin.close();
	fout.close();
	return 0;
}