#include <iostream>
#include <fstream>
#include <stack>
#include <vector>
#include <bitset>
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
vector <int> adiacenta[100001];
vector<int> rasp[100001];
stack<int>st;
int n,m,cnt,comp;
bitset<100001> viz,in_stack;
int low_link[100001],indice[100001];

int DFS(int nod)
{
    low_link[nod] = ++cnt;
    indice[nod] = cnt;
    viz[nod] = 1;
    st.push(nod);
    in_stack[nod]=1;
    for(auto x:adiacenta[nod])
    {
        if(!viz[x])
        {
            DFS(x);
        }
        else
            if(viz[x] && in_stack[x])
            {
                low_link[nod] = min(low_link[nod],low_link[x]);
            }
    }
    if(low_link[nod] == indice[nod])
    {
        comp++;
        while(1)
        {
            int curent = st.top();
            st.pop();
            in_stack[curent] = 0;
            rasp[comp].push_back(curent);
            if(low_link[curent] ==indice[curent])
            {
                break;
            }
        }
    }

}
int main()
{
    f >> n >> m;
    for(int i = 1; i<=m; i++)
    {
        int x,y;
        f >> x >> y;
        adiacenta[x].push_back(y);
    }

    for(int i = 1; i<=n; i++)
    {
        if(!viz[i])
        {
            DFS(i);
        }
    }
    g << comp<< '\n';
    for(int i = 1; i<=comp; i++)
    {
        for(auto x :rasp[i])
        {
            g << x << " ";
        }
        g << endl;
    }

}