#include<stdio.h>
#include<vector>

using namespace std;

vector <int> muchii[100004];
int grad_viz[100007];

int numar_noduri, numar_muchii;

void df(int nod){
	grad_viz[nod]=-1;
	for(unsigned int i=0;i<muchii[nod].size();i++)
		if(grad_viz[muchii[nod][i]]!=-1)
			df(muchii[nod][i]);
	
}

int main(){
	freopen("dfs.in","r",stdin);
	freopen("dfs.out","w",stdout);
	scanf("%d", &numar_noduri);
	scanf("%d", &numar_muchii);
	int x,y;
	
	for(int i=1;i<=numar_muchii;i++){
		scanf("%d", &x);
		scanf("%d", &y);
		muchii[x].push_back(y);
		
	}
	int nr=0;
	for(int i=1;i<=numar_noduri;i++)
		if(grad_viz[i]!=-1){
			df(i);
			nr++;
		}
		
	printf("%d", nr);
	
	return 0;
}