#include <iostream>
#include <cstdio>
#include <vector>
#include <stack>
#define Nmax 100010
using namespace std;

vector <int> Graf[Nmax];
vector <int> GrafT[Nmax];
stack <int> S;
int Viz[Nmax];
int NrC;
int N,M;

void Citire()
{
    int x,y;
    scanf("%d %d",&N,&M);
    for(int i=0;i<M;++i)
    {
        scanf("%d %d",&x,&y);
        Graf[x].push_back(y);
        GrafT[y].push_back(x);
    }
}


void DFS(int V)
{
    for(int i=0;i<Graf[V].size();++i)
    {
        int x=Graf[V][i];
        if(!Viz[x])
        {
            Viz[x]=-1;
            DFS(x);
        }
    }
    S.push(V);
}

void DFST(int V)
{
    Viz[V]=NrC;
    for(int i=0;i<GrafT[V].size();++i)
    {
        int x=GrafT[V][i];
        if(Viz[x]==-1)
            DFST(x);
    }
}


int main()
{
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);
    Citire();
    NrC=1;
    for(int i=1;i<=N;++i)
        if(!Viz[i])
        {
            Viz[i]=-1;
            DFS(i);
        }
    while(!S.empty())
    {
        int V=S.top();
        S.pop();
        if(Viz[V]==-1)
        {
            DFST(V);
            NrC++;
        }
    }
    printf("%d\n",NrC-1);
    bool ok=false;
    for(int i=1;i<=NrC;++i)
    {
        for(int j=1;j<=N;++j)
            if(Viz[j]==i)
            {
                ok=true;
                printf("%d ",j);
            }
        if(ok)
        {
            ok=false;
            printf("\n");
        }

    }
    return 0;
}