#include <cstdio>
#include<vector>
#include<algorithm>
#define MAX 100001
using namespace std;
int N,M,Cnt,Nrcomp;
int inStack[MAX],Low[MAX],Disc[MAX];
vector <int>CTC[MAX],Stack,Nod[MAX];

void Dfs(int k)
{
    Disc[k]=Low[k]=Cnt;
    Cnt++;
    Stack.push_back(k);
    inStack[k]=1;
    for(int i=0;i<Nod[k].size();i++)
    {
        int vec=Nod[k][i];
        if(Disc[vec]==-1)
        {
            Dfs(vec);
            Low[k]=min(Low[k],Low[vec]);
        }
        else
        {
            if(inStack[vec])
                Low[k]=min(Low[k],Disc[vec]);
        }
    }
    if(Low[k]==Disc[k])
    {
        int u;
        do
        {
            u=Stack.front();
            Stack.pop_back();
            inStack[u]=0;
            CTC[Nrcomp].push_back(u);
        }while(u!=k);
        Nrcomp++;
    }
}

int main()
{
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);
    scanf("%d%d",&N,&M);
    for(int i=1,x,y;i<=M;i++)
    {
        scanf("%d%d",&x,&y);
        Nod[x].push_back(y);
    }
    for(int i=0;i<=N;i++)
        Disc[i]=-1;
    for(int i=1;i<=N;i++)
    {
        if(Disc[i]==-1)
            Dfs(i);
    }
    printf("%d\n",Nrcomp);
    for(int i=0;i<Nrcomp;i++)
    {
        for(int j=0;j<CTC[i].size();i++)
            printf("%d ",CTC[i].front());
        printf("\n");
    }
    return 0;
}