#include <bits/stdc++.h>
#define Dmax 100005
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
int n,m,viz[Dmax],nrCTC;
vector<int>G[Dmax],sol[Dmax],GT[Dmax];
stack<int>S;

void DFS1(int nod)
{
    viz[nod] = 1;
    for(vector<int>::iterator it = G[nod].begin(); it < G[nod].end(); it++)
        if(!viz[*it])
        DFS1(*it);
    S.push(nod);
}

void DFS2(int nod)
{
    viz[nod] = 2;
    for(vector<int>::iterator it = GT[nod].begin(); it < GT[nod].end(); it++)
        if(viz[*it] == 1)
        DFS2(*it);
    sol[nrCTC].push_back(nod);
}

int main()
{
    f>>n>>m;
    for(int i = 1; i <= m; i++)
    {
       int x,y;
       f>>x>>y;
       G[x].push_back(y);
       GT[y].push_back(x);
    }
    for(int i = 1; i<=n; i++)
        if(!viz[i])
        DFS1(i);
    while(!S.empty())
    {
        int nod = S.top();
        S.pop();
        if(viz[nod] == 1)
        {
            nrCTC++;
        DFS2(nod);
        }
    }
    g<<nrCTC<<"\n";
    for(int i = 1; i <= nrCTC; i++,g<<"\n")
        for(vector<int>::iterator it = sol[i].begin(); it < sol[i].end(); it++)
            g<<*it<<" ";


    return 0;
}