/*
    Keep It Simple!
*/

#include <fstream>
#include <vector>
#include <list>
#include <stack>
#include <string>
#include <cmath>
#include <queue>
#include <vector>
#include <algorithm>
#include <iostream>
#include <set>
#include <cstring>

using namespace std;

ifstream fin("ctc.in");
ofstream fout("ctc.out");

#define ll long long
#define mp make_pair
#define fi first
#define se second
#define pb push_back

typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

const int kMaxN = 100005;

vector<int> G[kMaxN],TG[kMaxN];
stack<int> Kos_st;
set<int> CTC_G[kMaxN];
vector<int> ctctest[kMaxN];
int ctc[kMaxN];
int N,M;
int ctc_sz;

void ReadInput()
{
    fin >> N >> M;
    int x,y;
    for(int i=1; i<=M; ++i)
    {
        fin >> x >> y;
        G[x].pb(y);
        TG[y].pb(x);
    }
}

void FrontDFS(int node)
{
    ctc[node] = true;
    for(auto it : G[node])
        if(!ctc[it])
            FrontDFS(it);
    Kos_st.push(node);
}

void BackDFS(int node)
{
    ctc[node] = ctc_sz;
    ctctest[ctc_sz].pb(node);
    for(auto it : TG[node])
        if(!ctc[it])
            BackDFS(it);
}

void Kosaraju()
{
    for(int i=1;i<=N;++i)
        if(!ctc[i])
            FrontDFS(i);
    memset(ctc,0,sizeof(ctc));

    while(!Kos_st.empty())
    {
        int node = Kos_st.top();
        Kos_st.pop();
        if(ctc[node]) continue;
        ++ctc_sz;
        BackDFS(node);
    }
}

void BuildTree()
{
    for(int x=1; x<=N; ++x)
        for(auto y : G[x])
            if(ctc[x] != ctc[y])
            {
                CTC_G[ctc[x]].insert(ctc[y]);
            }
}

void Solve()
{
    ReadInput();
    Kosaraju();
  //  BuildTree();
    fout << ctc_sz << '\n';
    for(int i=1; i<=ctc_sz; ++i)
    {
        for(auto it:ctctest[i])
            fout << it << ' ';
        fout << '\n';
    }
}

int main()
{
    Solve();
    return 0;
}