#include<bits/stdc++.h>
using namespace std;
int n,m,inn[100009],out[100009],vis[100009],ans[100009];
vector<int>a[100009];
inline int dt(int x)
{
	if(ans[x])return ans[x];
	for(int i=0;i<a[x].size();i++)
	ans[x]+=dt(a[x][i]);
	if(!ans[x])return 1;
}
int main()
{
	freopen("chain_2016.in","r",stdin);
	freopen("chain_2016.out","w",stdout);
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;i++)
	{
		int ai,bi;
		scanf("%d%d",&ai,&bi);
		a[bi].push_back(ai);
		inn[ai]++;
		out[bi]++;
	}
/*	for(int i=1;i<=n;i++)
	for(int j=0;j<a[i].size();j++)
	cout<<a[i][j]<<" ";*/
	for(int i=1;i<=n;i++)
	if(!inn[i]&&out[i])dt(i);
	int cnt=0;
	for(int i=1;i<=n;i++)
	if(!inn[i]&&out[i])cnt+=ans[i];
	cout<<cnt;
      return 0;
  }