#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int MAXN=1e4+5;
const int INF=2147483647; 
int sum,low[MAXN],n,m,dfn[MAXN],cnt,grade[MAXN],head,ans,zx=INF;
bool vis[MAXN];
vector<int>from[MAXN],to[MAXN];
int bfs(int u,int k){
	if(dfn[u]){
		if(grade[u]!=k) head=low[u]-cnt;
		return low[u];
	}
	dfn[u]=low[u]=cnt++,grade[u]=k;
	for(int i=0;i<from[u].size();i++){
		low[u]=min(low[u],bfs(from[u][i],k)+head);
	}  
	return low[u]-head;
}
int main(){
	cin>>n>>m;
	for(int x,y,i=1;i<=m;i++){
		scanf("%d%d",&x,&y);
		from[y].push_back(x),to[x].push_back(y);
	}
	for(int i=1;i<=n;i++)
		if(!to[i].size())
			sum++;
	if(sum>=2){
		cout<<0;
		return 0;
	}
	for(int i=1;i<=n;i++)
		if(!dfn[i]){
			head=0,cnt=1;
			bfs(i,++ans);
		}
	for(int i=1;i<=n;i++){
		if(low[i]<zx) zx=low[i],sum=1;
		else if(low[i]==zx) sum++;
	}
	cout<<sum;
	return 0;
}