#include <stdio.h>
#include <vector>
#include <bitset>
#include <stack>
using namespace std;

stack<int> stac;

vector< vector<int> >G(100005);
int n,m;
bitset<100005> viz;
bitset<100005> inStack;

vector< vector<int> > scc;

int nr=1,num[100005],low[100005];
int min(int a,int b){return a<b?a:b;}

void dfs(int u){
	viz[u]=1;stac.push(u);inStack[u]=true;
	
	low[u]=num[u]=nr++;
	int v;
	for(int i=0;i<G[u].size();i++){
		v=G[u][i];
		if(!viz[v]){
			dfs(v);
			low[u]=min(low[u],low[v]);
		}
		else{
			if(inStack[v])
				low[u]=min(low[u],num[v]);
		}
	}
	if(low[u]==num[u]){
		vector<int> newV;
		while(true){
			v=stac.top();stac.pop();inStack[v]=false;
			newV.push_back(v);
			if(v==u) break;
		}
		scc.push_back(newV);	
	}
}

int main(){
	int x,y;
	freopen("ctc.in","r",stdin);
	freopen("ctc.out","w",stdout);
	scanf("%d",&n);scanf("%d",&m);
	for(int i=0;i<m;i++){scanf("%d",&x);scanf("%d",&y);G[x].push_back(y);}
	viz.reset();
	for(int i=1;i<=n;i++) if(!viz[i]) dfs(i);
	
	printf("%d\n",scc.size());
	
	for(int i=0;i<scc.size();i++){
		for(int j=0;j<scc[i].size();j++)
			printf("%d ",scc[i][j]);
		printf("\n");
	}
	return 0;
}