/**
    CTC-Tarjan
**/
#include<bits/stdc++.h>
#define maxN 100005
using namespace std;
int val,niv[maxN],low[maxN],st[maxN],vf,ctc,n,m,x,y;
bool InStack[maxN];
vector<int> v[maxN],C[maxN];
inline int min(int a,int b)
{
    return a<b?a:b;
}
void dfs(int nod)
{
    val++;
    niv[nod]=val;
    low[nod]=val;
    st[++vf]=nod;
    InStack[nod]=1;
    for(vector<int>::iterator it=v[nod].begin();it!=v[nod].end();it++)
    {
        if(!niv[*it])
        {
            dfs(*it);
            low[nod]=min(low[nod],low[*it]);
        }
            else
        if(InStack[*it])
            low[nod]=min(low[nod],low[*it]);
    }
    if(niv[nod]==low[nod])
    {
        ctc++;
        int x=st[vf];
        do
        {
            x=st[vf];
            C[ctc].push_back(x);
            vf--;
            InStack[x]=0;
        }while(x!=nod);
    }
}
int main()
{
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++)
    {
        scanf("%d%d",&x,&y);
        v[x].push_back(y);
    }
    for(int i=1;i<=n;i++)
        if(!niv[i]) dfs(i);
    printf("%d\n",ctc);
    for(int i=1;i<=ctc;i++)
    {
        for(vector<int>::iterator it=C[i].begin();it!=C[i].end();it++)
            printf("%d ",*it);
        printf("\n");
    }
    return 0;
}