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

int n,m;
vector <int> G[100001];
vector <int> Gi[100001];
vector <int> CTC[100001];
vector <int> :: iterator it;
int mark[100001], nodu[100001],k,k1;
void dfs1(int vf)
{
    vector <int> :: iterator it;
    mark[vf]=1;
    for (it=G[vf].begin();it!=G[vf].end();it++)
        {
            int i= (*it);
            if (mark[i]==0) dfs1(i);
        }

    nodu[++k]=vf;
}

void dfs2(int vf)
{
    vector <int> :: iterator it;
    mark[vf]=1;
    for (it=Gi[vf].begin();it!=Gi[vf].end();it++)
        {
            int i= (*it);
            if (mark[i]==0) dfs2(i);
        }

    CTC[k1].push_back(vf);
}

int main()
{
    vector <int> :: iterator it;
    FILE *f,*g;
    f=fopen("ctc.in","r");
    g=fopen("ctc.out","w");
    fscanf(f,"%d%d",&n,&m);
    int x,y;
    for (int i=1;i<=m;i++)
    {
        fscanf(f,"%d%d",&x,&y);
        G[x].push_back(y);
        Gi[y].push_back(x);
    }
    for (int i=1;i<=n;i++)
        if (mark[i]==0) dfs1(i);

    k1=0;

    for (int i=1;i<=n;i++)
        mark[i]=0;
    for ( int i=n;i>=1;i--)
        if (mark[nodu[i]]==0)
        {
            k1++;
            dfs2(nodu[i]);
        }
    fprintf(g,"%d\n",k1);
    for (int i=1;i<=k1;i++)
    {
        for (it=CTC[i].begin();it!=CTC[i].end();it++)
            {
                int j= (*it);
                fprintf(g,"%d ",j);
            }

        fprintf(g,"\n");
    }
    return 0;
}