#include<stdio.h>
#include<vector>
#include<stack>
#include<algorithm>
#include<list>
using namespace std;
#define nMax 100010
int n,m,nrSol,ind;
vector <int> a[nMax],ut(nMax,0);
vector <int> In(nMax,-1),low(nMax),r;
vector < vector <int> > rez;
stack <int> st;
void tarjan(int N)
{
	In[N]=low[N]=ind++;
	st.push(N);
	ut[N]=1;
	for(vector <int> ::iterator it=a[N].begin();it!=a[N].end();it++)
	{
		if(In[*it]<0)
		{
			tarjan(*it);
			low[N]=min(low[N],low[*it]);
		}
		else
			if(ut[*it])
			{
				low[N]=min(low[N],In[*it]);
			}
	}
	if(low[N]==In[N])
	{
		int x;
		r.clear();
		do
		{
			r.push_back(x=st.top());
			st.pop();
			ut[x]=0;
		}while(x!=N);
		rez.push_back(r);
	}
}
int main()
{
	freopen("ctc.in","r",stdin);
	freopen("ctc.out","w",stdout);
	scanf("%d%d",&n,&m);
	for(int i=0;i<m;i++)
	{
		int x,y;
		scanf("%d%d",&x,&y);
		a[x].push_back(y);
	}
	for(int i=1;i<=n;i++)
		if(In[i]<0)
			tarjan(i);
	printf("%d\n",(int)rez.size());
	for(int i=0;i<(int)rez.size();i++)
	{
		for(int j=0;j<(int)rez[i].size();j++)
			printf("%d ",rez[i][j]);
		printf("\n");
	}
	return 0;
}