#include<bits/stdc++.h>
using namespace std;
int n,m;
int df[100003],in[100003],out[100003];
vector<int>vec[100003];
int sum=0;
int dfs(int x)
{
	if(df[x])return df[x];
	else {
		for(int i=0;i<vec[x].size();i++)
		 df[x]+=dfs(vec[x][i]);
		//cout<<df[x]<<endl;
		return df[x];
	}
}
int main()
{
	freopen("chain_2016.in","r",stdin);
	freopen("chain_2016.out","w",stdout);
	cin>>n>>m;
	int a,b;
	memset(df,0,sizeof(df));
	for(int i=1;i<=m;i++)
	{
		scanf("%d%d",&a,&b);
		vec[a].push_back(b);
		in[b]++,out[a]++;
	}
	for(int i=1;i<=n;i++)
	if(in[i]&&!out[i])df[i]=1;
	for(int i=1;i<=n;i++)
	if(!in[i]&&out[i])sum+=dfs(i);
	cout<<sum;
}