#include <stdio.h>
#include <vector>
#define N 100001
using namespace std;
vector<int> a[N];
int n,m,nr,t;
int tin[N],tout[N],v[N];
void DFS(int nod)
{
	tin[nod]=t++;
	int i;
	v[nod]=1;
	for (i=0;i<a[nod].size();i++) 
	{
			int y = a[nod][i];
			if (v[a[nod][i]]==0) 
				DFS(y);
	}
	tout[nod]=t++;
}	
int main()
{
	int i,x,y;
	freopen("dfs.in","r",stdin);
	freopen("dfs.out","w",stdout);
	scanf("%d%d",&n,&m);
	for (i=1;i<=m;i++)
	{
		scanf("%d%d",&x,&y);
		a[x].push_back(y);
	}
	for (i=1;i<=n;i++) if (v[i]==0) 
	{
		nr++; 
		DFS(i);
	}
	printf("%d\n",nr);
	return 0;
}