#include <cstdio>
#include <vector>
#include <queue>

using namespace std;

#define maxN 100005
#define PB push_back

int N , M;
bool viz[maxN];

vector <int> lista[maxN];

void dfs (int nod)
{
	if (viz[nod]) return;
	
	viz[nod] = true;
	
	
	for (unsigned int i = 0 ; i < lista[nod].size () ; ++i)
	{
		int nodcur = lista[nod][i];
		
		if (viz[nodcur]) continue;
		
		dfs (nodcur);
	}
}


int main ()
{
	freopen ("dfs.in" , "r" , stdin);
	freopen ("dfs.out" , "w" , stdout);
	
	scanf ("%d %d" , &N , &M);
	
	
	int a , b;
	
	for (int i = 1 ; i <= M ; ++i)
	{
		scanf ("%d %d" , &a , &b);
		
		lista[a].PB (b);
	}
	
	
	int comp = 0;
	
	for (int i = 1 ; i <= N ; ++i)
	{
		if (viz[i]) continue;
		
		dfs (i);
		++comp;
	}
	
	printf ("%d" , comp);
	
	return 0;
}