/// Kosaraju's algorithm
#include <iostream>
#include <fstream>
#include <vector>
#include <string.h>

#define NMax 100001

using namespace std;

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

int N,M;
vector<int> G[NMax],T[NMax],sol[NMax];
bool mark[NMax];
int stack[NMax],K,nr;

void Read();
void Write();

void DFS1(int node)
{
    mark[node]=true;
    for(vector<int>::iterator it=G[node].begin();it!=G[node].end();it++)
        if(mark[*it]==false)
            DFS1(*it);
    stack[++K]=node;
}

void DFS2(int node)
{
    sol[nr].push_back(node);
    mark[node]=true;
    for(vector<int>::iterator it=T[node].begin();it!=T[node].end();it++)
        if(mark[*it]==false)
            DFS2(*it);
}

int main()
{
    Read();

    for(int i=1;i<=N;i++)
        if(mark[i]==false)
            DFS1(i);
    memset(mark,false,sizeof(mark));
    for(int i=K;i>0;i--)
        if(mark[stack[i]]==false)
        {
            nr++;
            DFS2(stack[i]);
        }

    Write();

    return 0;
}

void Read()
{
    fin>>N>>M;
    for(int i=1;i<=M;i++)
    {
        int x,y;
        fin>>x>>y;
        G[x].push_back(y);
        T[y].push_back(x);
    }
}

void Write()
{
    fout<<nr<<"\n";
    for(int i=1;i<=nr;i++)
    {
        for(vector<int>::iterator it=sol[i].begin();it!=sol[i].end();it++)
            fout<<*it<<" ";
        fout<<"\n";
    }
}