十万火急！！1

#include<bits/stdc++.h>
using namespace std;
struct sd{
	vector<int>fa;
	int num,id;
	long long ans;
}node[100005];
int n,m,a,b,du[100005],now;
long long res;
queue<int>q;
int main()
{
	scanf("%d%d",&n,&m);
	while(m--)
	{
		scanf("%d%d",&a,&b);
		node[min(a,b)].fa.push_back(max(a,b));
		du[max(a,b)]++;node[max(a,b)].num++;
	}
	for(int i=1;i<n;++i)
	if(!du[i]&&!node[i].fa.empty()) node[i].ans=1,q.push(i);
	while(!q.empty())
	{
		now=q.front();
		for(int i=0;i<node[now].fa.size();++i)
		{
			node[node[now].fa[i]].num-=1;
			node[node[now].fa[i]].ans+=node[now].ans;
			if(node[node[now].fa[i]].num==0) q.push(node[now].fa[i]);
		}
		q.pop();
	}
	for(int i=1;i<n;++i)
	{ res=max(res,node[i].ans);} 
	printf("%lld",res);
}