#include <bits/stdc++.h>

using namespace std;

ifstream in("ctc.in");
ofstream out("ctc.out");

vector<int> graf[100005];
vector<int> ans[100005];

stack<int> st;
int a[100005],b[100005];
bool instack[100005];
int t,ans1;
void tarjan(int x)
{
	t++;
	a[x]=t;
	b[x]=t;
	st.push(x);
	instack[x]=1;
	for(auto k:graf[x])
	{
		if(a[k]==0)
		{
			tarjan(k);
			b[x]=min(b[x],b[k]);
		}
		else if(instack[k])
			b[x]=min(b[x],b[k]);
	}
	if(b[x]==a[x])
	{
		while(!st.empty() && b[x]<=b[st.top()])
		{
			ans[ans1].push_back(st.top());
			instack[st.top()]=0;
			st.pop();
		}
		ans1++;
	}
}
int main()
{
	int n,m;
	in>>n>>m;
	for(int i=1;i<=m;i++)
	{
		int x,y;
		in>>x>>y;
		graf[x].push_back(y);
	}
	for(int i=1;i<=n;i++)
		if(a[i]==0)
			tarjan(i);
	out<<ans1<<"\n";
	for(int i=0;i<ans1;i++)
	{
		for(int j=0;j<ans[i].size();j++)
			out<<ans[i][j]<<" ";
		out<<"\n";
	}
	return 0;
}