#include<stdio.h>
#include<vector>
#include<stack>

#define maxn 100005
#define pb push_back

using namespace std;

FILE*f=fopen("ctc.in","r");
FILE*g=fopen("ctc.out","w");

int n,m,index;
int niv[maxn],lowest[maxn],viz[maxn],inSt[maxn];
vector<int>G[maxn],v;
vector< vector<int> >C;
stack<int>St;

inline void citire () {
	
	fscanf(f,"%d %d",&n,&m);
	
	int x,y;
	for ( int i = 1 ; i <= m ; ++i ){
		fscanf(f,"%d %d",&x,&y);
		G[x].pb(y);
	}
}

inline void componenta ( int x ){
	v.clear();
	int nod;
	
	do{
		nod = St.top(); inSt[nod] = 0; St.pop();
		v.pb(nod);
	}while(nod != x);
	
	C.pb(v);
}

void dfs ( int nod ){
	viz[nod] = 1; St.push(nod); inSt[nod] = 1;
	++index;
	niv[nod] = lowest[nod] = index;
	
	for ( vector<int>::iterator itt = G[nod].begin() ; itt != G[nod].end() ; ++itt ){
		int nodvcn = (*itt);
		
		if ( !viz[nodvcn] ){
			dfs(nodvcn);
			lowest[nod] = min(lowest[nod],lowest[nodvcn]);
		}
		else{
			if ( inSt[nodvcn] ){
				lowest[nod] = min(lowest[nod],lowest[nodvcn]);
			}
		}
	}
	
	if ( lowest[nod] == niv[nod] ){
		componenta(nod);
	}
}

inline void ctc () {
	
	for ( int i = 1 ; i <= n ; ++i ){
		if ( !viz[i] ){
			dfs(i);
		}
	}
	
	fprintf(g,"%d\n",C.size());
	for ( int i = 0 ; i < C.size() ; ++i ){
		for ( vector<int>::iterator itt = C[i].begin() ; itt != C[i].end() ; ++itt ){
			fprintf(g,"%d ",*itt);
		}
		fprintf(g,"\n");
	}
}

int main () {
	
	citire();
	ctc();
	
	fclose(f);
	fclose(g);
	
	return 0;
}