#include<stdio.h>
#include<vector>
#define NM 100005
using namespace std;
vector <int> G[NM];
int viz[NM],n,m,i,cc,n1,n2;
void dfs(int nod)
{
	viz[nod]=1;
	int N=G[nod].size();
	for(int j=0;j<N;j++)
		if(!viz[G[nod][j]])
			dfs(G[nod][j]);
}
int main()
{
	freopen("dfs.in","r",stdin);
	freopen("dfs.out","w",stdout);
	scanf("%d %d",&n,&m);
	for(i=1;i<=m;i++)
	{
		scanf("%d %d",&n1,&n2);
		G[n1].push_back(n2);
	}
	for(i=1;i<=n;i++)
		if(!viz[i])
		{
		++cc;
		dfs(i);
		}
	printf("%d",cc);
	return 0;
}